ARTÍCULO

Contribution to the knowledge of the natural hybrids of the genera Aeonium and Greenovia (Crassulaceae) in La Gomera, Canary Islands

OCTAVIO ARANGO

c. Loreto 24-26, Escalera B, 4º 2ª, ES-08029 Barcelona, Spain

ORCID iD. O. ARANGO: https://orcid.org/0000-0002-9712-5402

E-mail: oja.oja@hotmail.com

Editor: L. Sáez

ABSTRACT
Contribution to the knowledge of the natural hybrids of the genera Aeonium and Greenovia (Crassulaceae) in La Gomera, Canary Islands.— As part of a chorological and eco-biological study carried out in La Gomera with the nine species, two subspecies, and two varieties that make up the genera Aeonium and Greenovia, seven new hybrids were discovered. These add to the ten hybrids previously described by other authors on the island. The botanical descriptions of five new hybrids are provided. Since we only know the vegetative parts in the remaining two, some chorological, morphological, and taxonomic data are disclosed and photographically illustrated. A differential diagnosis of the new hybrids with other previously described nothotaxa on the island is made, especially with those that share one of the parents. The nomenclatural types were deposited in the LPA and TFC Canary herbaria.
KEY WORDS: Aeonium; Canary Islands; chorology; ecology; Greenovia; La Gomera; new hybrids; taxonomy.

RESUMEN
Contribución al conocimiento de los híbridos naturales de los géneros Aeonium y Greenovia (crassulaceae) en La Gomera, Islas Canarias.— Como parte del estudio fitocorológico y eco-biológico realizado en La Gomera con las nueve especies, dos subespecies y dos variedades que componen los géneros Aeonium y Greenovia, fueron descubiertos siete híbridos nuevos, que se suman a los 10 híbridos anteriormente descritos por otros autores en la isla. Se aportan las descripciones botánicas completas en cinco de los nuevos híbridos descubiertos, y en los dos restantes, puesto que solo conocemos la parte vegetativa, se dan a conocer algunos datos corológicos, morfológicos y taxonómicos, y se ilustran fotográficamente las plantas. Se hace el diagnóstico diferencial de los nuevos híbridos con otros nototaxones descritos anteriormente en la isla, especialmente con los que compartían alguno de los parentales. Los tipos nomenclaturales fueron depositados en los herbarios canarios LPA y TFC.
PALABRAS CLAVE: Aeonium; corología; ecología; Greenovia; Islas Canarias; La Gomera; nuevos híbridos; taxonomía.

CONTENIDOS

INTRODUCTIONTop

Of all the genera that make up the rich and varied flora of the Canary Islands, Aeonium Webb & Berthel. has the largest number of species (Bramwell & Bramwell, 2001Bramwell, D. & Bramwell, Z. 2001. Flores silvestres de las Islas Canarias (4th ed.). Editorial Rueda, Madrid. ; Acebes-Ginovés et al., 2010Acebes-Ginovés J. R., León-Arencibia M. C., Rodríguez-Navarro L., del Arco-Aguilar M., García-Gallo A., Pérez de Paz P. L., Rodríguez-Delgado O., Martín-Osorio V. E. & Wildpret de la Torre W. 2010. Pteridophyta, Spermatophyta. In: Arechavaleta M., Rodríguez S., Zurita N. & García A. (Coords.). Lista de especies silvestres de Canarias. Hongos, plantas y animales terrestres. 2009. Gobierno de Canarias, Santa Cruz de Tenerife.; Schönfelder & Schönfelder, 2018Schönfelder, P. & Schönfelder, I. 2018. Flora Canaria. Guía de identificación. Editorial Turquesa, Santa Cruz de Tenerife.; BIOTA, 2021BIOTA [Gobierno de Canarias. Banco de Datos de Biodiversidad de Canarias] 2021. Retrieved November 5, 2021, from http://www.biodiversidadcanarias.es/biota ; Sauerbier et al., 2023Sauerbier, H., Cabrera, F. & Mauer, T. 2023. Flora vascular de Canarias. Editorial Turquesa, Santa Cruz de Tenerife.) and has undoubtedly generated the largest number of natural hybrids in the entire archipelago, with about 80 known nothotaxa. Although hybrids of the genus Aeonium usually disappear from nature in the first filial generation, they can produce gene dilution in the pure species with which they coexist since pollen viability in some hybrids is 80–90% (Liu, 1989Liu, H.-Y. 1989. Systematics of Aeonium (Crassulaceae). Special Publication 3. Natural Museum of Natural Science. Taichung, Taiwan.), which compromises their reproduction and makes them more vulnerable to various threats in the wild (Levin et al., 1996Levin, D. A., Francisco-Ortega, J. & Jansen, R. K. 1996. Hybridization and extinction of rare plant species. Conservation Biology 10: 10–16. https://doi.org/10.1046/j.1523-1739.1996.10010010.x; Francisco-Ortega et al., 2000Francisco-Ortega, J., Santos-Guerra, A., Kim, S. C. & Crawford, D. J. 2000. Plant genetic diversity in the Canary Islands: a conservative perspective. American Journal of Botany: 909–919. https://doi.org/10.2307/2656988; Brilhante et al., 2021Brilhante, M., Roxo, G., Catarino, S., Dos Santos, P., Reyes-Betancort, A., Caujapé-Castells, J., Meneses Sequeira, M., Talinhas, P. & Romeiras, M. M., 2021. Diversification of Aeonium species across Macaronesian Archipelagos: correlations between genome-size variation and conservation status. Frontiers in Ecology and Evolution 9: 607338. https://doi.org/10.3389/fevo.2021.607338). Therefore, it is important to recognize them in nature, describe them, and deposit material well-preserved in the herbarium collections since these can contribute to understanding the phylogeny and evolution of this group of plants.

The rugged orography, the wide altitudinal range, the enormous variety of habitats, and the rich diversity of vegetation make La Gomera an optimal natural laboratory for chorological and eco-biological studies, such as the one we have carried out with the genera Aeonium Webb & Berthel. and Greenovia Webb & Berthel. As can be seen in the work of Voggenreiter (1999Voggenreiter, V. 1999. Fitocorología de las 11 especies y sus híbridos de Aeonium Webb & Berth. y de Greenovia diplocycla Webb ex Bolle en La Gomera, Islas Canarias (Crassulaceae). Vieraea 27: 27–44.), the genus Aeonium is widely represented on La Gomera and has 12 taxa distributed throughout the island. While the genus Greenovia is only represented by G. diplocycla Webb ex Bolle, which is distributed over a large part of the island.

So far, ten natural hybrids previously described by other authors were known, and in this work, seven new hybrids discovered on the island have been added, four between species of Aeonium and three intergeneric hybrids between Aeonium and Greenovia (Table 1). We do not agree with the fusion of the genera Aeonium and Greenovia based solely on molecular parameters without considering the outstanding morphological and functional characters that differentiate the two genera (Arango, 2021aArango, O. 2021a. Greenovia millennium (Crassulaceae): una nueva especie y sus híbridos. Tenerife, Islas Canarias. Botánica Macaronésica 31: 11–32., 2023bArango, O. 2023b. Greenovia ignea y Aeonium calderense (Crassulaceae): dos nuevas especies de La Palma, Islas Canarias. Botánica Macaronésica 32: 145–166.). Therefore, the crosses between Aeonium and Greenovia in this work have been treated as intergeneric hybrids, according to the ICNB regulations (Turland et al., 2018Turland, N. J., Wiersema, J. H., Barrie, F. R., Greuter, W., Hawksworth, D. L., Herendeen. P. S., Knapp, S., Kusber, W.-H., Li, D.-Z., Marhold, K., May, T. W., McNeill, J., Monro, A. M., Prado, J., Price, M. J. & Smith, G. F. (Eds.) 2018. International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code) adopted by the Nineteenth International Botanical Congress Shenzhen, China, July 2017 (Regnum Vegetabile, 159). Koeltz Botanical Books, Glashütten. https://doi.org/10.12705/Code.2018).

An inductive analysis of the data obtained in this research project, and in the study of many natural hybrids in the other mountainous islands of the archipelago (T, P, GC, H), show that the only two effective reproductive barriers in the genus Aeonium are the allopatry of the species and the different flowering time (Arango 2015Arango, O. 2015. Aeonium ×claperae (Crassulaceae), un nuevo híbrido natural de Tenerife (Islas Canarias). Vieraea 43: 329–334. , 2016aArango, O. 2016a. Confirmación experimental del rango de especie para Aeonium mascaense Bramwell (Crassulaceae). Botánica Macaronésica 29: 25–34., bArango, O. 2016b. Aeonium ×wildpretii Bañares (Crassulaceae): descripción de la flor, nueva localidad y actualización taxonómica. El Hierro, Islas Canarias. Botánica Macaronésica 29: 83–89. , 2017Arango, O. 2017. Aeonium ×monteaquaense, A. ×afurense y A. ×marreroi (Crassulaceae), tres nuevas notoespecies de las Islas Canarias. Vieraea 45: 267–284. https://doi.org/10.31939/vieraea.2017.45.15, 2019aArango, O. 2019a. Descripción de cuatro nuevas notoespecies del género Aeonium (Crassulaceae) en las Islas Canarias y aportaciones corológicas y nomenclaturales al género. Vieraea 46: 115–146. https://doi.org/10.31939/vieraea.2019.46.tomo01.06, bArango, O. 2019b. Aeonium liui (Crassulaceae): una nueva especie de Tenerife, Islas Canarias. Botánica Macaronésica 30: 7–22., cArango, O. 2019c. Descripción de Aeonium ×exsul (Crassulaceae). Un viejo nombre para un nuevo híbrido natural de Tenerife (Islas Canarias). Botánica Macaronésica 30: 143–152., 2021aArango, O. 2021a. Greenovia millennium (Crassulaceae): una nueva especie y sus híbridos. Tenerife, Islas Canarias. Botánica Macaronésica 31: 11–32., bArango, O. 2021b. Confirmación experimental del rango de especie de Aeonium mascaense (Crassulaceae). (Addenda). Botánica Macaronésica 31: 33–40., cArango, O. 2021c. Nuevas aportaciones al género Aeonium (Crassulaceae): descripción de cinco notoespecies nuevas y ampliación corológica. Islas Canarias. Vieraea 47: 157–192. https://doi.org/10.31939/vieraea.2021.47.07, 2023aArango, O. 2023a. Descripción de Aeonium ×gulliveri (Crassulaceae), un nuevo y singular híbrido de La Palma, Islas Canarias. Botánica Macaronésica 32: 167–174.). This is because the transfer of pollen through biotic and abiotic pollinators does not work between disjunct geographic areas. These observations are part of a series of fundamental and constant rules governing F1 hybridization in the genus Aeonium, which have been synthesized and will published separately.

The overall results of this research have been divided into two articles for publication. The first article includes the results related to the natural history and the rules governing F1 hybridization in the genus Aeonium (O. Arango, unpubl. data). This second article presents the taxonomic results of the work, and whose main objective is to describe and illustrate seven new nothotaxa discovered in the genus Aeonium in La Gomera.

MATERIAL AND METHODSTop

Based on the areal distribution of the species that compose the genera Aeonium and Greenovia in La Gomera provided by Voggenreiter (1999Voggenreiter, V. 1999. Fitocorología de las 11 especies y sus híbridos de Aeonium Webb & Berth. y de Greenovia diplocycla Webb ex Bolle en La Gomera, Islas Canarias (Crassulaceae). Vieraea 27: 27–44.), fieldwork was carried out at numerous points of the island to collect chorological, ecological, and reproductive biology data of the taxa of both lineages and their hybrids. Special attention was paid to the identification of new nothotaxa not known to science.

The search for new hybrids was carried out according to the targeted search method developed previously (Arango, 2021cArango, O. 2021c. Nuevas aportaciones al género Aeonium (Crassulaceae): descripción de cinco notoespecies nuevas y ampliación corológica. Islas Canarias. Vieraea 47: 157–192. https://doi.org/10.31939/vieraea.2021.47.07). The method consists of three steps: (1) the distribution of all the species in the island was taken from Voggenreiter (1999Voggenreiter, V. 1999. Fitocorología de las 11 especies y sus híbridos de Aeonium Webb & Berth. y de Greenovia diplocycla Webb ex Bolle en La Gomera, Islas Canarias (Crassulaceae). Vieraea 27: 27–44.) and later authors; (2) for each pair of species with overlaps in their areas of distribution, the literature was searched to check whether hybrids between them had been described; (3) for those species pairs that did not have hybrids described, the areas of overlap were extensively searched for potential hybrids. The new nothotaxa were recognized by having been found living inter parentes and by the morphological characteristics they presented, according to those characters with taxonomic value used by Praeger (1929Praeger, R. L. 1929. Semperviva of the Canary Islands area. Proceedings of the Royal Irish Academy 38B: 454–499. , 1932Praeger, R. L. 1932. An account of the Sempervivum group (Reprint, 2012). Plant Monograph reprints J. Cramer & H. K. Swann, Stuttgart.) and Liu (1989Liu, H.-Y. 1989. Systematics of Aeonium (Crassulaceae). Special Publication 3. Natural Museum of Natural Science. Taichung, Taiwan.) in the genus Aeonium. When plants were not flowering at the time of discovery, they were monitored in situ or grown until flowering. A differential diagnosis of the new hybrids was made by comparing them with the protologues of hybrids published by other authors in La Gomera, and with their herbarium types, especially when there was a coincidence between any of the parents. The study of fresh specimens and herbarium sheets was carried out using a stereoscopic microscope of 4–8X magnification. Metric data were obtained with an electronic digital caliper (Digital Caliper BV001, Ireland CE) and small structures were measured on millimeter paper under the stereoscopic magnifier. The exact color of the flowers was established by comparison with the Pantone® color palette (http/www.pantone-colours.com/). All new hybrids were photographed in digital format and the iconography is available to those interested in Aeonium hybrids. The types were deposited at LPA and TFC.

RESULTS AND DISCUSSIONTop

Aeonium ×dendroides Arango nothosp. nov.

[Aeonium decorum var. decorum Webb ex Bolle × Aeonium saundersii Bolle]. Fig. 1

Figure 1. Aeonium ×dendroides Arango nothosp. nov.: (A), aspect of the plant in its habitat; (B), inflorescence (photographs: O. Arango) [View full size] [Descargar tamaño completo]

Holotype: Spain, Canary Islands: La Gomera, El Atajo, near Embalse de Chegelipes, 320 m, 28º 07′ 05′′ N, 17º 10′ 07′′ W, 02.I.2015, O. Arango (TFC 53260). Isotype: ibid., El Atajo, near Embalse de Chegelipes, 02.I.2015, O. Arango (LPA 40744–40745).

Diagnosis: Aeonium ×dendroides differs from A. ×praedictum Arango by the miniature tree-like plant habit, 20 cm tall, smaller rosettes (7–10 cm), fully pubescent obovate-cuneate leaves like those of A. saundersii Bolle; smaller inflorescence (8–10 cm long), lax, with creamy-yellow flowers, and all floral structures provided with glandular pubescence. Likewise, it differs from ×Greenonium lajense Arango, another hybrid of the area with the participation of A. saundersii, since the plants have a greater number of branches arranged in the form of a miniature tree; the flowers are 8 parted, cream yellow, and all the floral structures are pubescent. Finally, it differs from A. ×beltranii Bañares (TFC 19946!), a hybrid present in the area in which A. decorum Webb ex Bolle participates, by the branched habit of the plants, by the shape and size of the leaves, because the inflorescence is much smaller, with few flowers and these are creamy yellow.

Description: perennial subshrub plant, intermediate in size between the parents, 15–20 cm tall, consisting of a basal stem that divides mid-height into 3–5 branches, which divide progressively, giving the appearance of a miniature tree. Leaf rosette flattened, 7–10 cm in diameter, lax. Phyllotaxy: 3/8. Leaves ovate-cuneate, pubescent, light green, 5 × 2 × 0.4 cm, acute apex and cuneate base, margin provided in the distal half with short conical cilia and glandular hairs interspersed. Inflorescence in lax panicle, 8–10 cm high, pubescent, with bracts as a smaller leaf in the lower part and 2–3 floriferous branches, each with 8–10 flowers. Calyx with elongated triangular sepals, 3.5 × 1.5 mm, densely pubescent. Flowers with 8 (7–9) parted, radial flat corolla, 2.2 cm in diameter; petals linear-lanceolate, cream-yellow and greenish on the underside, 9 × 2.5 mm, pubescent. Stamens white with cylindrical glabrescent filaments and rounded gold yellow anthers. Carpels white, glabrescent, with ovaries 3 × 1 mm; styles 3 mm long, moderately divergent. Nectariferous scales absent. Fig. 2.

Figure 2. Aeonium ×dendroides Arango nothosp. nov.: (A), plant habit; (B), inflorescence; (C), leaves and leaf margin detail; (D), flowers and flower buds; (E), petals on both sides and stamens; (F), carpels; (G), seeds (drawing: O. Arango). [View full size] [Descargar tamaño completo]

Phenology: Flowering April to June.

Etymology: The infraspecific epithet derives from the Greek déndron: tree, and eidés: form, alluding to the small tree-like appearance of the plants.

Habitat: It is a sporadic natural hybrid that was found living among parentals in rocky slopes, dry, and sunny habitats, on the Canary vegetation belt of the thermosclerophyllous forest, 200–800 m.

Aeonium ×praedictum Arango nothosp. nov.

[Aeonium decorum var. decorum Webb ex Bolle × Aeonium gomerense (Praeger) Praeger]. Fig. 3.

Figure 3. Aeonium ×praedictum Arango nothosp. nov.: (A), aspect of the plant growing in its habitat; (B), inflorescence (photographs: O. Arango). [View full size] [Descargar tamaño completo]

Holotype: Spain, Canary Islands: La Gomera, road GM-1 (old part TF-711), near Degollada de San Sebastian, 572 m, 28º 07′ 45′′ N, 17º 10′ 32′′ W, 08.I.2015, O. Arango (LPA 40746). Paratype: ibid., road GM-1, near Degollada de San Sebastian, 580 m, O. Arango (TFC 54562).

Diagnosis: The differential diagnosis of A. ×praedictum includes A. ×aguajilvense Bañares (TFC 37963!), an extremely rare hybrid that we have never seen in nature; however, an analysis of the protologue and the study of the holotype, confirms that these are two different nothotaxa. The new hybrid differs from A. ×aguajilvense because the plants consist of a central stem ending in a dominant rosette of larger size (10–12 cm) and 4 to 6 shaped-chandelier branches ending in smaller rosettes. The leaves are yellowish-green similar to those of A. decorum; the inflorescence is a conical panicle, glabrous, with bell-shaped flowers, broad petals in a left-contorted arrangement with the margin provided with glandular hairs, the filaments of the stamens are flat tapering. Likewise, A. ×praedictum differs from A. ×castellodecorum Bañares (TFC 19944!), another hybrid of the area with the participation of A. decorum, because the plants of the new hybrid are much less branched and the rosettes are larger (10–12 cm), the leaves are oblanceolate-cuneate, glabrescent, yellowish-green with a red border and the margin is provided in the distal half with conical cilia; the flowers have broad petals and are not laterally twisted as is usual in A. castello-paivae Bolle hybrids.

Description: Perennial subshrub plant, intermediate in size between the parents, 25–35 cm tall, formed by a central stem ending in a main rosette, which at mid-height divides into 4–6 shaped-chandelier branches. Leaf rosette flattened, 10–12 cm in diameter, lax. Phyllotaxy: 5/13. Leaves oblanceolate-cuneate, glabrate, dark green with a red border, 7 × 2.2 × 0.5 cm, apiculate obtuse apex, cuneate base, margin provided on distal half with conical cilia 0.5 mm long. Inflorescence in conical panicle, 18 × 20 cm, glabrous central axis provided with bracts similar to smaller leaves, and 12–15 dichotomous floral branches in the distal in two floriferous branches, each with 8–10 flowers. Calyx with elongated triangular sepals, 6 × 2 mm, glabrate. Flowers with 8 (7–9) parted, bell-shaped corolla, 2.0–2.2 cm in diameter; petals lanceolate, acuminate, 10 × 3 mm, glabrescent on the margin and abaxially, white with pink hues on the underside, in a left-contorted arrangement. Stamens white with flattened glabrescent filaments and yellow pale rounded anthers. Carpels with white ovaries, glabrous, 4.0 × 1.2 mm; styles 4.0 mm long, white, glabrous, divergent in the distal part and capitate stigmas. Nectariferous scales white, quadrangular in shape, 1.0 × 0.8 mm apically undulate. Fig. 4

Figure 4. Aeonium ×praedictum Arango nothosp. nov.: (A), plant habit; (B) inflorescence; (C) leaves and leaf margin detail; (D), flowers and flower buds; (E), levo-contorta arrangement of petals in the corolla; (F), petals on both sides and stamens; (G), carpels; (H), nectariferous scales; (I), seeds (drawings: O. Arango). [View full size] [Descargar tamaño completo]

Phenology: Flowering April to June.

Etymology: The epithet infraspecific refers to botanist Volker Voggenreiter’s prediction that human action would make this hybrid possible in nature.

Habitat: It is a sporadic natural hybrid that was found living in a rocky and sunny area, on the Canary vegetation belt of the thermosclerophyllous forest, 200–800 m.

The distribution areas of A. gomerense (Praeger) Praeger and A. decorum var. decorum Webb ex Bolle, which previously did not coincide spatially, came into contact due the effect that Voggenreiter (1999Voggenreiter, V. 1999. Fitocorología de las 11 especies y sus híbridos de Aeonium Webb & Berth. y de Greenovia diplocycla Webb ex Bolle en La Gomera, Islas Canarias (Crassulaceae). Vieraea 27: 27–44.) called “anthropogenic translocation following roads” which favored the progressive colonization of roadsides by A. decorum bringing the populations of both parents closer together and as predicted by the German botanist, hybridization between.

Aeonium ×pendulum Arango nothosp. nov.

[Aeonium saundersii Bolle × Aeonium spathulatum (Hornemann) Praeger]. Fig. 5.

Figure 5. Aeonium ×pendulum Arango nothosp. nov.: (A), aspect of the plant growing in its habitat; (B), inflorescence (photographs: O. Arango). [View full size] [Descargar tamaño completo]

Holotype: Spain, Canary Islands: La Gomera, near Roque de Agando, 1050 m., 05.V.2012, O. Arango (TFC 53312).

Diagnosis: Aeonium ×pendulum differs from A. ×holospathulatum nothovar. sanchezii Bañares, (TFC 19945!) the other hybrid from La Gomera with the participation of A. spathulatum (Hornemann) Praeger, by the pendulous habit of the plants, formed by numerous thin intertwined stems ending in a single small (5–8 cm), flat rosettes that become globose in the dry season; the inflorescence is ostensibly smaller (5–6 cm high), with only 3 to 5 non-dichotomous floral branches, each with 5–7 large greenish-yellow pubescent flowers.

Description: Perennial subshrub plant, pendulous habit, intermediate in size between the parents, 40–50 cm long, consisting of a short basal stem that divides successively into numerous intertwined thin stems. Leaf rosette flattened, 5–8 cm in diameter, lax. Phyllotaxy: 3/8. Leaves spatulate-cuneate, pubescent, light green, 3 × 2 × 0.3 cm, rounded apex, cuneate base, margin with rounded cilia and glandular hairs interspersed. Inflorescence small, lax, 6 × 5 cm long, densely glandular-pubescent, provided with bracts like smaller leaves, and 3–5 dichotomous floral branches each with 5–7 flowers in progressive anthesis. Calyx with elongated ensiform-linear sepals, 5 × 1 mm, densely pubescent. Flowers with 11 (10–12) parted, radial flat corolla, 1.8–2.0 cm in diameter, petals lanceolate, acute apex apiculate, 8 × 2 mm, glabrous, greenish-yellow. Stamens are yellow with cylindrical glabrous filaments and rounded pale yellow anthers. Carpels with barrel-shaped, greenish-yellow ovaries, glabrescent, 3 × 2 mm; styles 3 mm long, glabrous, not divergent. Nectariferous scales absent. Fig. 6.

Figure 6. Aeonium ×pendulum Arango nothosp. nov.: (A), plant habit; (B), inflorescence; (C), leaves and leaf margin detail; (D), flowers and flower buds; (E), petals on both sides and stamens; (F), carpels (drawing: O. Arango). [View full size] [Descargar tamaño completo]

Phenology: Flowering April to June.

Etymology: The infraspecific epithet refers to the pendulous habit of plants.

Habitat: It was found growing among the parents in a rocky habitat with little exposure to the sun, on the Canary vegetation belt of the humid forest of Pinus canariensis Chr. Sm. ex DC., 800–1200 m.

×Greenonium haeckelii Arango nothosp. nov.

[Greenovia diplocycla Webb ex Bolle × Aeonium castello-paivae Bolle]. Fig. 7.

Figure 7. ×Greenonium haeckelii Arango nothosp. nov.: (A), aspect of the plant growing in its habitat; (B), inflorescence (photographs: O. Arango). [View full size] [Descargar tamaño completo]

Holotype: Spain, Canary Islands: La Gomera, Hermigua, Barranco de Monteforte, near Embalse de Mulagua, 260 m, 08.V.2014, O. Arango, (TFC 53309). Paratype: ibid., Barranco de Monteforte, near Embalse de Mulagua, O. Arango (LPA 40742–40743).

Diagnosis: ×Greenonium haeckelii differs from ×G. lajense, another intergeneric hybrid described in this article, in that the plants of ×G. haeckelii are sparsely or not branched (0–2). The central stem ends in a larger dominant rosette (12–15 cm); the leaves are spatulate-cuneate, glaucous green like the parents; the inflorescence is larger and with a greater number of floral branches (6–8), the flowers have 10 parted, the petals are linear-lanceolate distinctively glandular pubescence on the margin and abaxially. Likewise, ×G. haeckelii differs from ×G. laxiflorum J. M. Macarrón & Bañares (TFC 25003!), another intergeneric hybrid of G. diplocycla, because the plants of the new hybrid are sparsely branched, generally consisting of a single large rosette, the leaves are glaucous green; the inflorescence is distinctly a cymose anthela, provided with leaf-like bracts that do not imbricate each other and, only 4–5 floral branches; the flowers are pale yellow, the petals are slender and exhibit glandular pubescence at the margin and abaxially. Fig. 8.

Figure 8. ×Greenonium haeckelii Arango nothosp. nov.: (A), plant habit; (B), inflorescence; (C), leaves and leaf margin detail; (D), flowers and flower buds; (E), petals on both sides and stamens; (F), carpels (drawings: O. Arango). [View full size] [Descargar tamaño completo]

Description: perennial subshrub plant, intermediate size between the parents, 10–12 cm tall, formed by a single basal woody stem which is sometimes divided into 1 or 2 branches ending in a single rosette. Main leaf rosette cup-shaped, 12–15 cm in diameter. Phyllotaxy: 5/13. Leaves spatulate-cuneated, concave, glabrescent, 6.0 × 3.0 × 0.3 cm, glaucous green color and multiple tannic lines on the underside; leaf margin subtly hyaline, provided with short conical cilia in the distal part and glandular hairs interspersed. Inflorescence in a cymose anthela, with the main axis ending in a larger central flower, glandular-pubescent, 15 × 20 cm long, provided with obovate-cuneate bracts, and 6–8 dichotomous floral branches. Calyx dialysepal, glandular-pubescent, elongated triangular sepals 4 × 2 mm. Flowers with 9–12 parted, radial flat corolla, 1.8–2.0 cm in diameter; petals linear-lanceolate, acuminate, pale yellow, 8 × 2 mm, pubescent abaxially and distinctively provided with glandular hairs on the margin; stamens with cylindrical filaments, glabrescent, anthers deltoid-rounded, pale yellow. Carpels with yellowish-white ovaries, entirely pubescent, 2.0 × 1.5 mm; styles glabrescent, 2.0 mm long, divergent. Nectariferous scales absent. Fig. 8

Phenology: Flowering April to May.

Etymology: The infraspecific epithet was named in honor of the German naturalist Ernst Haeckel, who conducted Ecology and Marine Biology studies on Canary Island in the 19th century (Sarmiento, 2011Sarmiento, M. 2011. La expedición científica de Ernst Haeckel a Lanzarote (1866-1867). Las Canarias en la Teoría de la Evolución. Editorial Encasa, Málaga.).

Habitat: It was found living between the parents in sunny, stony soil, on the Canary vegetation belt of the thermosclerophyllous forest, 200–800 m.

×Greenonium lajense Arango nothosp. nov.

[Greenovia diplocycla Webb ex Bolle × Aeonium saundersii Bolle]. Fig. 9.

Figure 9. ×Greenonium lajense Arango nothosp. nov.: (A), appearance of the plant growing in its habitat; (B), inflorescence (photographs: O. Arango). [View full size] [Descargar tamaño completo]

Holotype: Spain, Canary Islands: La Gomera, La Laja, Route 29 towards El Bailadero, 780 m, 28º 06′ 59′′ N, 17º 11′ 53′′ W, 18.V.2014, O. Arango (TFC 53309).

Diagnosis: ×Greenonium lajense differs from ×G. laxiflorum, another intergeneric hybrid involving A. decorum because the plants of the new hybrid consisting of a main stem that at the top divides into 5 or 6 branches in verticillate arrangement, ending in smaller rosettes (6–8 cm), with olive-green, orbicular-cuneate leaves, densely pubescent like those of A. saundersii and the margin devoid of cilia; the inflorescence is a cymose anther (6–8 cm tall), with the central axis provided with non-imbricate bracts and 4 or 5 floral branches, each with 6–10 larger flowers (2.4 cm), with 17–18 parted and glabrous petals. For differential diagnosis with ×G. haeckelii, another intergeneric hybrid described in this article, see the diagnosis of this nothotaxon.

Description: Perennial subshrub plant, intermediate size between the parents, 18–20 cm tall, formed by a main woody stem dividing at the top into 4–6 verticillate branches. Leaf rosette cup-shaped, lax, 6–8 cm in diameter. Phyllotaxy: 5/13. Leaves orbicular-cuneate in mature plants, 4.0 × 3.0 × 0.2 cm, densely pubescent glandular, light green color, and leaf margin slightly hyaline, provided only with glandular hairs. Inflorescence in a cymose anthela with the main axis ending in a larger central flower, 8 × 16 cm height, glandular-pubescent, provided by leaf-like bracts, and 4–5 arcuate floral branches dichotomous in the distal third in two floriferous branches each with 6–10 flowers. Calix densely glandular-pubescent, with 3 × 1 mm linear-ensiform sepals. Flowers with 18 parted, radial flat corolla, 2.2–2.4 cm in diameter; petals oblanceolate, apiculate, apex acute, 8 × 3 mm, glabrous, dark yellow; stamens with cylindrical, glabrous, yellow-green filaments, anthers ovoid, bright yellow. Carpels with yellow-green ovaries, 2.8 × 2.0 mm, entirely pubescent; glabrescent styles, 2.5 mm long, slightly divergent. Nectariferous scales absent. Fig. 10.

Figure 10. ×Greenonium lajense Arango nothosp. nov.: (A), plant habit; (B), inflorescence; (C), leaves and leaf margin detail; (D), flowers and flower buds; (E), petals on both sides and stamens; (F), carpels; (G), seeds (drawings: O. Arango) [View full size] [Descargar tamaño completo]

Phenology: Flowering April to May.

Etymology: The infraspecific epithet refers to La Laja, the locality where it was discovered.

Habitat: It was found living between the parentals in a shady habitat on the Canary vegetation belt of the humid forest, 700–1000 m.

Finally, we provide some data and illustrations of two other natural hybrids from La Gomera, A. ×rhombifolium Arango and ×Greenonium cabrerae A. Santos nothovar. ojilense, of which we only know the vegetative part of the plant. Therefore, we will postpone the complete description until we have the flowers.

Aeoniun ×rhombifolium Arango nothosp. nov.

[Aeonium decorum var. decorum Webb ex Bolle × Aeonium lindleyi Webb & Berthel. subsp. viscatum (Bolle) Bañares]. Fig. 11.

Figure 11. Aeonium ×rhombifolium Arango nothosp. nov.: (A), the appearance of the plant growing in a basaltic rock fissure in its habitat; (B), red circle: remains of an inflorescence showing how the central axis ends in a single flower forming a cymose panicle (photographs: O. Arango). [View full size] [Descargar tamaño completo]

Location: Spain, Canary Islands: La Gomera, near the village of El Atajo, 167 m, 04.II.2020, O. Arango.

Etymology: The infraspecific epithet refers to rhombus-shaped leaves.

Habitat: Aeonium ×rhombifolum is a sporadic natural hybrid that was found living between the parents in the fissure of a compact basaltic rock, in the transition zone between the Canary vegetation floors of xerophytic scrub and thermosclerophyllous forest, 100–400 m.

Discussion: This is a rare hybrid in nature despite being a cross between two very common species that share extensive areas on the island’s western side. Possibly its rarity is because the floral phenology of the parents does not coincide in time, or that the specimens are not recognizable in the nature due to the morphological convergence generated by backcrossing with the parents. We finally recognized this hybrid in its habitat thanks to a specimen that conserved its floral remains, in which the central axis of the inflorescence ended in a single central flower of larger size (Fig. 11B). This is a character undoubtedly inherited from A. lindleyi Webb & Berthel. subsp. viscatum (Bolle) Bañares, whose inflorescence is described as a cymose panicle (Liu, 1989Liu, H.-Y. 1989. Systematics of Aeonium (Crassulaceae). Special Publication 3. Natural Museum of Natural Science. Taichung, Taiwan.). In addition, the leaves were rhomboid-spatulate, the lamina finely puberulent and the leaf margin devoid of cilia. These characters also link it to A. lindleyi subsp. viscatum, although the plant habit was reminiscent of A. decorum.

In the literature reviewed, we found only one mention of this hybrid, and that was in a book for succulent plant amateurs (Carbonell, 2007Carbonell, E. 2007. Cuadernos de suculencia. Bejeques y siemprevivas. Editorial Ciape, Barcelona.), which succinctly stated: “A. ×selentenius (A. decorum × A. viscatum)”, without providing any information on the hybrid or the source of the reference. Nor is this name mentioned in the portal Especies Vegetales en Canarias (2022Especies Vegetales en Canarias 2022. Retrieved February 17, 2023, from https://endemicascanarias.com/index.php/es) the only Canarian biodiversity database that provides information on natural hybrids; nor in the POWO (2017POWO [Plants of the Word Online] 2017. Retrieved June 28, 2022, from https://powo.science.kew.org/) the world’s largest portal of published plants. For all these reasons, we consider that it is a nomen nudum, Art. 41.7, Note 3, Ex. 23, of the ICNB (Turland et al., 2018Turland, N. J., Wiersema, J. H., Barrie, F. R., Greuter, W., Hawksworth, D. L., Herendeen. P. S., Knapp, S., Kusber, W.-H., Li, D.-Z., Marhold, K., May, T. W., McNeill, J., Monro, A. M., Prado, J., Price, M. J. & Smith, G. F. (Eds.) 2018. International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code) adopted by the Nineteenth International Botanical Congress Shenzhen, China, July 2017 (Regnum Vegetabile, 159). Koeltz Botanical Books, Glashütten. https://doi.org/10.12705/Code.2018).

×Greenonium cabrerae A. Santos nothovar. ojilense Arango nothovar. nov.

[Greenovia diplocycla Webb ex Bolle × Aeonium spathulatum (Hornemann) Praeger]. Fig. 12.

Figure 12. ×Greenonium cabrerae Santos nothovar. ojilense Arango nothovar. nov. The right side of the photo: the new hybrid growing in its habitat. The left side: Greenovia diplocycla, one of the parentals (photographs: O. Arango). [View full size] [Descargar tamaño completo]

Location: Spain, Canary Islands: La Gomera, path PR-LG 17, near the Roque de Ojila, 1120 m, 24.I.2020, O. Arango. Fig. 12.

Etymology: The epithet that refers to Roque de Ojila, the site where it was discovered.

Discussion: The hybrid ×Greenonium cabrerae Santos (TFC 37964!), was described on the island of La Palma by Santos (1983Santos Guerra, A. 1983. Flora y vegetación de La Palma. Editorial Interinsular Canaria, Santa Cruz de Tenerife.), we recently found a vicariant nothovariety of this hybrid in an area of canary pine forest near the Roque de Ojila on La Gomera. The only morphological differences observed concerning the La Palma hybrid were that the plants have fewer branches, the rosettes are slightly smaller, and the leaves are wider with the apex rounded, but these differences may be due to the environmental conditions in which they grow and have no taxonomic value.

Habitat: ×Greenonium cabrerae nothovar. ojilense is a sporadic natural hybrid that was found growing among the parentals in a wet soil with limited sunshine at the edge of the pine forest, on the Canary vegetation floor of the pine forest, of Pinus canariensis, 800–1200 m.

ACKNOWLEDGEMENTSTop

I thank Carlos Pedrós-Alió, professor and research scientist at CSIC in Madrid for his time spent on critical reading of the manuscript, as his comments improved this paper considerably. I am grateful to Cristina González Montolongo of the Department of Botany, Ecology and Plant Physiology of the University of La Laguna for the access she has always given me to consult the sheets of the TFC Herbarium, the most complete collection of natural hybrids of the genus Aeonium and Greenovia of the world.

REFERENCESTop

APPENDIX. Additional specimens examined from Flora of the Canary Islands.Top

Additional material studied

Spain, Canary Islands, El Hierro: Aeonium ×holospathulatum Á. Bañares. [A. arboreum (L.) Webb & Berthel. var. holochrysum Ho-Yih Liu × A. spathulatum (Hornemann) Praeger], near San Andrés, III.1989, Á. Bañares (TFC 3974). Ibidem, San Andrés, 1020 m, 29.V.2012, O. Arango (deposited in LPA). La Gomera: Aeonium ×aguajilvense Á. Bañares, [A. castello-paivae Bolle × A. gomerense (Praeger) Praeguer], Aguajilva, 700 m, V.1991, Á. Bañares (TFC 37963). Aeonium ×beltranii Á. Bañares, [A. decorum Webb ex Bolle × A. subplanum Praeger], El Bailadero, 950 m, III.1981, Á. Bañares (TFC 19946). Aeonium ×bravoanum Bramw. & Rowl. [A. castello-paivae Bolle × A. decorum Webb ex Bolle], El Bailadero, 950 m, V.1983, Á. Bañares (TFC 19944). Tamargada, 350 m, VI.1983, C. Rios Jordana (TFC 9951). Aeonium ×castellodecorum Á. Bañares [A. castello-paivae Bolle × A. decorum Webb ex Bolle], El Bailadero, 950 m, V.1983, Á. Bañares (TFC 19944). Aeonium decorum Webb mss, Barranco del Agua, Valle de San Sebastian, IV.1845, Bourgeau, (FI 000088). Aeonium gomerense (Praeger) Praeguer, without locality, 8.V.1951, E. R. Sventenius (ORT 5621). Ibidem, Cumbre Carbonera, 950m, VI.1996, Á. Bañares, E. Carqué & M. Marrero (TFC 38718). Aeonium ×perezerii Á. Bañares, [A. decorum Webb ex Bolle × A. urbicum subsp. urbicum (Chr. Sm. ex Buch) Webb & Berth.], Barranco de Benchejigua, 600 m, IV.1985, Á. Bañares (TFC 25024). Aeonium sedifolium Webb Pit. & Pr., Masca, E. R. Sventenius (ORT 12400). ×Greenonium laxiflora J. M. Macarrón & Á. Bañares, [Greenovia diplocycla Webb ex Bolle × A. decorum Webb ex Bolle], Barranco de La Laja, 550 m, III.1987, Á. Bañares (TFC 25003). La Palma: Aeonium ×cabrerae Santos ex Á. Bañares, [Greenovia diplocycla Webb ex Bolle × A. spathulatum (Hornemann) Praeger], Las Manchas (supra Jedey), 1000 m, VII.1990, Á. Bañares (TFC 37964). Tenerife: Aeonium ×holospathulatum Á. Bañares. [A. holochrysum Webb & Berthel. × A. spathulatum (Hornemann) Praeger var. spathulatum], Arafo, 950 m, III. 1981, Á. Bañares (TFC 19949).