﻿Gesneriatuberifera (Gesneriaceae), a new lithophytic species from the Sierra de Bahoruco, Barahona Peninsula of southern Hispaniola (Dominican Republic)

﻿Abstract A narrowly endemic new species of Gesneria is described from the Sierra de Bahoruco in the Dominican Republic’s Barahona Peninsula of southern Hispaniola. Gesneriatuberifera J.L.Clark & T.Clase, sp. nov. differs from all other congeners by the presence of a tuber and tubular red corollas with yellow lobes. Images and a discussion are provided to summarize the presence of tubers in other Gesneriaceae and differentiate Gesneriatuberifera from congeners that share a lithophytic habit. Based on IUCN guidelines, a preliminary conservation status of Endangered (EN) is assessed for G.tuberifera.


Introduction
The flowering plant family Gesneriaceae, with over 3400 species and 150+ genera (Weber 2004;Weber et al. 2013), is in the order Lamiales.The family is divided into three subfamilies and seven tribes (Weber et al. 2013(Weber et al. , 2020)), each of which represent monophyletic lineages (Ogutcen et al. 2021).Most Neotropical members are in the subfamily Gesnerioideae, which is represented by 1200+ species and 77 genera (Clark et al. 2020).Gesneria L. is classified in the tribe Gesnerieae and subtribe Gesneriinae Oerst.(Weber et al. 2013(Weber et al. , 2020)).
The subtribe Gesneriinae is strongly supported as a monophyletic clade that is mostly Caribbean and includes the following three genera: Gesneria, PhytoKeys 235: 43-52 (2023), DOI: 10.3897/phytokeys.235.110476John L. Clark & Teodoro Clase: Gesneria tuberascens (Gesneriaceae), a new lithophytic species from the DR Pheidonocarpa L.E.Skog, and Rhytidophyllum Mart.Pheidonocarpa has one species with a subspecies endemic to Cuba and a second subspecies endemic to Jamaica.Rhytidophyllum is mostly endemic to the Caribbean islands, with the exception of two species in northern South America.Gesneria is entirely endemic to the Caribbean region and was most recently monographed by Skog (1976).Updated circumscriptions to several broadly defined species in Skog (1976) were re-circumscribed in publications by Clark et al. (2019), Lambert et al. (2017), andJoly et al. (2023).The addition of Gesneria tuberifera brings the total species diversity of Gesneria to 63 or 73 taxa when including infraspecific ranks.
Gesneria is broadly characterized by alternate leaves, an inferior or sub-inferior ovary, and glabrous filaments that are substantially free (adnate at base only) from the corolla tube.The habit for Gesneria is variable, but most species are perennial subshrubs (lithophytes or terrestrial) or lithophytes with leaves in a rosette.The corolla shape in Gesneria ranges from tubular to campanulate.The base chromosome number for all members of the tribe Gesnerieae is n = 14 (Lee 1966(Lee , 1968), a character that supports the monophyly of Gesneria, Pheidonocarpa L.E.Skog, and Rhytidophyllum.The flowers of Gesneria are usually zygomorphic.Gesneria radiata J.L.Clark & Cinea is a recently described species (Joly et al. 2023) and is the only species in the genus with corollas that appear radially symmetrical.
Plants were photographed in the field and subsequently pressed and dried.Specimens were deposited at the Jardín Botánico Nacional ''Dr.Rafael M. Moscoso'' (JBSD), Marie Selby Botanical Gardens (SEL), United States National Herbarium (US), New York Botanical Garden (NY), Missouri Botanical Garden (MO), and other herbaria.Photographs were taken of live specimens in the field using a Nikon D7200 DSLR camera, Nikon 105mm lens, and Nikon SB-29s ring flash.Morphological observations and measurements were made from live collections, alcohol-preserved material, and digital images using the ImageJ program (Schneider et al. 2012).
The extinction risk for Gesneria tuberifera was assessed following the IUCN (2012) and guidelines of the IUCN Standards and Petitions Committee (2022).Observations, collection localities, and population estimates from fieldwork were considered when assessing the IUCN category.Species area of occupancy (AOO) was calculated using GeoCAT (Bachman et al. 2011) with the default setting of a 2 km 2 grid (extent of occurrence (EOO) was not calculated because of the limited number of known populations).

Taxonomic treatment
Gesneria tuberifera J.L.Clark & T.Clase, sp.nov.urn:lsid:ipni.org:names:77330583-1Fig. 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.
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).

(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 km 2 .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.

Figure 1 .
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.