Gesneria tuberifera J.L.Clark & T.Clase, 2023

Clark, John L. & Clase, Teodoro, 2023, Gesneria tuberifera (Gesneriaceae), a new lithophytic species from the Sierra de Bahoruco, Barahona Peninsula of southern Hispaniola (Dominican Republic), PhytoKeys 235, pp. 43-52 : 43

Gesneria tuberifera J.L.Clark & T.Clase sp. nov.

Fig. 1

Diagnosis.

Differs from all other Gesneria by the presence of a tuber. Additional characters that differentiate G. tuberifera from congeners is a rosette of leaves, elongate red tubular corollas with yellow lobes, and a lithophytic habit.

Type.

Dominican Republic. Pedernales: Sierra de Bahoruco, Las Mercedes, km 28 on the road Cabo Rojo-Aceitillar , Cañada La U, 18°7'13.05"N, 71°37'25.09"W, 840 m, 26 Jan 2023, J.L. Clark & T. Clase 17279 (holotype: JBSD; isotypes: FLAS, MO, MT, NY, SEL, US) .

Description.

Unbranched lithophyte with well-developed woody tubers to 3.5 cm in diameter, older individuals with elongate woody shoots to 30 cm long subtending a rosette of leaves, younger individuals with short shoots (<5 cm long) with leaves in a basal rosette, apex of shoots covered with dense red pilose trichomes, base of shoots glabrescent. Leaves alternate, always clustered (rosette), coriaceous, petioles 0.5-1.0 cm long, velutinous, reddish; blade cuneate to broadly obovate, 5-8.5 × 1.5-2.5 cm, base attenuate, apex acute, margin sparsely serrate with 6-10 shallow lobes that become more deeply lobed near apex, margin of leaf with evenly spaced white trichomes, abaxially light green, densely pilose along main vein, especially near base, sparsely pilose along main vein near leaf apex, adaxially dark green, glabrous, lateral veins 6-9 per side. Inflorescence reduced to a single axillary flower, pedicel uniformly red, erect to horizontal, 3-5 cm long, in the upper axils. Floral tube obconic, 2-4 × 2-3 mm, uniformly red, shallowly sulcate with five ridges. Calyx lobes five, erect, 3-5 mm long, 2 mm wide, triangular, uniformly red. Corolla zygomorphic, uniformly tubular to slightly constricted apically, 2.2-2.7 cm long, 1-1.5 cm wide, mostly red with yellow lobes, limb with five erect lobes, subequal, semi-orbiculate, 1-2 × 1.5-2.5 mm, entire. Androecium with four stamens, 1.9-2.5 cm long, briefly adnate to the base of the corolla tube, included; anthers oblong, 1.0-2.5 × 1.0-1.5 mm; staminode present. Gynoecium with inferior ovary, disc annular, white; immature ovary globose, mature ovary not observed (flowers protandrous). Fruit a sub-woody globose bivalved capsule, 4-6 × 3-5 mm. Seeds fusiform, striated, twisted, 0.5-1.0 × 0.3 mm, dark brown to black.

Phenology.

Mature flowers were documented during January, February, June, and August. Mature fruits were documented during January, February, June, and August.

Etymology.

The specific epithet means growing a tuber and is derived from the presence of a swollen stem base (Fig. 1C ), a vegetative character consistent throughout the two populations observed during a 2023 field expedition to the Dominican Republic.

Distribution and preliminary assessment of conservation status.

Gesneria tuberifera is endemic to the Sierra de Bahoruco or Bahoruco mountain range in the Dominican Republic’s Barahona Peninsula of southern Hispaniola. The Sierra de Bahoruco is in the southwestern region of the Dominican Republic, adjacent to the southern border with Haiti, and encompasses the provinces of Pedernales and Barahona. Some parts of Sierra de Bahoruco comprise a national park, Sierra de Bahoruco National Park (Parque Nacional Sierra de Bahoruco). The park is recognized by the United Nations Educational, Scientific and Cultural Organization (UNESCO) as a Biosphere reserve. The forest is classified as humid forest (bosque húmedo) transitioning to broadleaf forest to pine (bosque latifoliado al pinar) in a riverside forest of a ravine (bosque ribereño de una cañada). Common woody plants in the ravine include Cassia spectabilis DC. ( Fabaceae ), Comocladia P.Browne ( Anacardiaceae ), Ficus L. sp. ( Moraceae ), Mastichodendron sp. (Engl.) H.J.Lam ( Sapotaceae ), Ocotea sp. Aubl. ( Laureaceae ), Oxandra sp. A.Rich ( Annonaceae ), Pinus occidentalis Sw. ( Pinaceae ), and Sloanea L. ( Elaeocarpaceae ).

There are two documented populations of Gesneria tuberifera , and both are south of the Sierra de Bahoruco National Park. Thus, there are no known populations of G. tuberifera within the Sierra de Bahoruco National Park or other protected areas. The two populations of G. tuberifera are within relatively easy access to major roads. The population from the type locality (Pedernales) includes approximately 100 individuals, covering a vertical limestone outcrop. The population from Enríquillo (Barahona) was more limited, with fewer than 50 individuals. The area of occupancy (AOO) was calculated as 12 km2. Following the IUCN Red List Categories and Criteria ( IUCN 2012) and guidelines of the IUCN Standards and Petitions Committee (2022), Gesneria tuberifera is preliminarily assessed as Endangered (EN), which is supported by a restricted population of less than 250 mature individuals (D).

Comments.

Most Gesneria taxa are multibranched terrestrial or lithophytic shrubs, 1-2 m tall. There are fewer than 10 species of Gesneria with a lithophytic habit with leaves in a rosette. Rosette-forming here is broadly defined to include taxa where there is a basal rosette of leaves without a developed stem (Fig. 1B, E ), a growth habit typical of many herbaceous annuals. In addition, rosette-forming can also describe perennial elongate shoots that might reach a length of 30 cm where an apical rosette of leaves is produced (Fig. 2E ). It is common in older individuals of lithophytic Gesneria taxa to develop unbranched elongate shoots that subtend rosettes of leaves. In contrast, lithophytic shrubs are often branched, reach 2 meters in height, but never form rosettes or clusters of leaves. Gesneria tuberifera includes individuals with basal rosettes of leaves (Fig. 1E ) and individuals with unbranched elongate shoots (ca. 30 cm long) subtending a terminal rosette of leaves.

A recent phylogenetic study by Joly et al. (2018) strongly supported the presence of several clades of shrubs (terrestrial or lithophytic) with hummingbird specialist pollination syndromes, but only one clade (fig. 6 in Joly et al. 2018) correlates with obligate lithophytes with leaves in a rosette. Many of the lithophytic rosette taxa are similar to Gesneria tuberifera , such as G. acaulis L. (Fig. 2B ) from Jamaica, G. cuneifolia (DC.) Fritsch from Puerto Rico, G. pedicellaris Alain (Fig. 2G ) from Dominican Republic, G. purpurascens Urb. (Fig. 2H ) from Cuba, G. reticulata (Griseb.) Urb. (Fig. 2C, D ) from Puerto Rico and Hispaniola, and G. yamuriensis Britton & P.Wilson from Cuba. Other Gesneria lithophytes with leaves in a rosette that were not represented in the phylogeny in Joly et al. (2018) include Gesneria christii Urb. (Fig. 2A ) from Hispaniola and G. libanensis Linden ex C. Morren (Fig. 2E, F ) from Cuba. Gesneria tuberifera differs from all other lithophytes with a rosette of leaves by the presence of tubers (Fig. 1C ) and tubular red corollas with yellow lobes (Fig. 1A ). In contrast, most lithophytic Gesneria with rosette leaves have uniformly red tubular corollas (Fig. 2 ) without contrasting coloration on the lobes.

The presence of tubers is relatively rare in Gesneriaceae . The only large genus (65+ species) where tubers are common is Sinningia Nees mainly from Brazil, which includes the commonly cultivated species Sinningia speciosa (Lodd.) Hiern (Fig. 3E, F ). Several small genera have tubers such as the monotypic genus Lembocarpus Leeuwenb. and Rhoogeton Leeuwenb. (2 species). Tubers are also present in Pachycaulos , a genus that was recently expanded ( Clark et al. 2023) to include two species, Pachycaulos huancabambae J.L.Clark & Moonlight and P. nummularia (Hanst.) J.L.Clark & J.F.Smith (Fig. 3G, H ). The tribe Sphaerorrhizeae was established by Roalson and Boggan ( Roalson et al. 2005) to accommodate a small clade of four species that are partly characterized by “stringy” rhizomes with tuber-like swellings. Other examples of tubers in Gesneriaceae are limited to single taxa within genera that are not usually tuberous. For example, Chrysothemis friedrichsthaliana (Hanst.) H.E. Moore forms tubers (Fig. 2A, B ), but their presence is inconsistent. Even when actively looking for tubers in wild populations of Chrysothemis friedrichsthaliana , their presence is sometimes completely absent or present in only a few individuals. Tubers are mostly absent in Trichodrymonia , but one exception is Trichodrymonia pedunculata (L.E.Skog) M.M.Mora & J.L.Clark where tubers are consistently present in cultivation and in the wild (Fig. 3C, D ) in eastern Panama. The presence of tubers in Gesneria tuberifera is the first documented example of this unusual character in the genus and it represents the only member of Gesneriaceae with tubers from the Caribbean.

The presence of tubers is mostly unknown in the Old World members of Gesneriaceae . The recently described monotypic genus, whose single species, Michaelmoelleria vietnamensis F.Wen, Z.B.Xin & T.V.Do, was not reported to have tubers when it was described from field collections ( Wen et al. 2020), but horticulturists have noticed tubers in cultivation (D. Zaitlin, pers. comm.). Weber (2004) provides a comprehensive survey on the range of morphological features documented throughout Gesneriaceae , and reports that tubers are confined to the New World Gesneriaceae . Thus, the presence of tubers in Michaelmoelleria F.Wen, Y.G.Wei & T.V.Do is the first and only known species of Old World Gesneriaceae with tubers.

Additional specimens examined.

Dominican Republic. Barahona: Sierra de Bahoruco, road from the coastal town of Enriquillo towards the community Blanco , area known locally as El Fondo Farallon , adjacent to Rio Fondo , 17°57'39.04"N, 71°13'50.16"W, 407 m, 28 Jan 2023, J.L. Clark et al. 17312 (FLAS, JBSD, MO, MT, NY, SEL, US); Sierra de Bahoruco, Municipio Enríquillo, seccion Los Blancos, paraje El Fondo, subiendo hacia loma Materesa, 600 m, 11 Jun 2009, B. Peguero et al. 4717 (JBSD) . Pedernales: Sierra de Bahoruco, road Cabo Rojo-Las Mercedes, Finca de Isabel , 18°06'50.09"N, 71°37'10.14"W, 738 m, 26 Jan 2023, J.L. Clark & T. Clase 17284 (FLAS, JBSD, MO, MT, NY, SEL, US); Sierra de Bahoruco, sección Las Mercedes, Aceitillar, subiendo en la carretera Cabo Rojo, 18°6'8.04"N, 71°37'14.3"W, 400-500 m, 10 Jun 2007, T. Clase et al. 4526 (JBSD); Sierra de Bahoruco, km 26 Norte desde el Puerto de Cabo Rojo (de la Alcoa Exploration Company) en el camino minero a Las Mercdes y Aceitillar, 18°06'N, 71°36'W, 610 m, 16 Feb 1982, T. Zanoni, M. Mejía, J. Pimentel & J.T. Mickel 19068 (JBSD, NY); Sierra de Bahoruco, entre los kms. 25-28 de la Carretera Puerto de Cabo Rojo hacia Aceitillar, 18°06'N, 71°37'W, 820 m, 1 Aug 1984, M. Mejía, J. Pimentel & R. García 1076 (JBSD) .

Figures

Figure 1. Gesneria tuberifera J. L. Clark & T. Clase A lateral view of mature flower B lithophytic habit C tuber with foliage D abaxial leaf surface E mature fruit (A, B J. L. Clark 17279 C J. L. Clark 17284 E J. L. Clark 17312). Photos by John L. Clark.

Figure 2. Gesneria taxa with lithophytic habits and elongate tubular red corollas A Gesneria acaulis L. B Gesneria christii Urb. C, D Gesneria reticulata (Griseb.) Urb. E, F Gesneria libanensis Linden ex C. Morren G Gesneria pedicellaris Alain H Gesneria purpurascens Urb. (A J. L. Clark 14532 B T. Talpey s. n. C, D J. L. Clark 17420 E, F J. L. Clark 15987 G J. L. Clark 17934 H J. L. Clark 12769). Photos by John L. Clark

Figure 3. Gesneriaceae taxa with tubers A, B Chrysothemis friedrichsthaliana (Hanst.) H. E. Moore C, D Trichodrymonia pedunculata (L. E. Skog) M. M. Mora & J. L. Clark E, F Sinningia speciosa (Lodd.) Hiern ' Niemeyer' G, H Pachycaulos nummularia (Hanst.) J. L. Clark & J. F. Smith (A, B J. L. Clark 12699 C, D J. L. Clark 12680 E, F D. Zaitlin s. n. G, H J. L. Clark 16357). Photos A, B, C and D by John L. Clark and photos E, F by David Zaitlin.