A new species of Dorstenia L. (Moraceae), D. luamensis M.E.Leal, is described from the Luama Wildlife Reserve, west of Lake Tanganyika and north of the town of Kalemie in the eastern part of the Democratic Republic of Congo (DRC). This species is endemic to the region and differs from any of the other species by its fernlike lithophytic habit and lack of latex. A description and illustration of this species is presented here. Dorstenia luamensis M.E.Leal inhabits moist and shady vertical rock faces close to small waterfalls in the forest; the species is distributed in small populations within the type locality, and merits the conservation status of endangered (EN).

Dorstenia , Albertine Rift, endemic, lithophytic

In 2012, a specimen of Dorstenia L. was collected from the Luama Wildlife Reserve in eastern DRC (M.E. Leal 2551) hanging from vertical cliffs and rock faces close to a waterfall on the shear zone of two figaus. These plants have a typical Dorstenia L. inflorescence but their hanging habit and lack of latex is unusual. The only other hanging Dorstenia species (hemi-epiphyte) is D. astyanactis Aké Assi first described from Ivory Coast (Ake Assi 1967) and later also collected in Cameroon (Pollard et al. 2003). Its inflorescence only has one appendix whereas the specimens from Luama have between 8 to12 appendices. The only other species in Africa mentioned in the revision of Berg and Hijmans (1999) growing on rocks is D. zanzibarica Oliver, but this species has dentate leaves and its receptacle is triangular to subquadrangular.

The specimens collected in the Luama Wildlife Reserve keyed out to the section of Kosaria using Berg and Hijman (1999) key to the sections of Dorstenia based on the two rows of appendages, short ones in the inner and longer ones in the outer row. Ignoring its hanging herbaceous habit, the specimens keyed out closest to D. benguellensis Welw. in the key to “Succulent and semi-succulent species of the Old World” (Bergman and Hijman 1999). They also mention in the species description that D. benguellensis Welw. grows “often among rocks” close to water courses and that its morphology is highly variable.

Therefore in this study, I compared the specimens collected from the Luama Wildlife Reserve with D. benguellensis Welw. to determine: 1) whether differences are insignificant and the existing description of D. benguellensis Welw. should be broadened to incorporate these specimens, or 2) whether differences are significant and these specimens should be described as a separate species. I argue that differences beyond habit are significant and that they merit their own status as a new species from the Luama Wildlife Reserve, D. luamensis M.E.Leal.

The collected specimens from the Luama Wildlife Reserve were compared to D. benguellensis Welw. following terminology and description format of Berg and Hijman (1999). Similarly, characteristics used in the Berg and Hijman (1999) key were applied to validate whether these specimens from the Luama Wildlife Reserve were significantly different from similar species within section Kosaria. The website Global Plants (www.plants.jstor.org) was also consulted to identify and measure specimens of Dorstenia collected and entered into the database after the publication of Berg and Hijman (1999).

Table 1 shows the description of D. benguellensis Welw. and the specimens collected in the Luama Wildlife Reserve. Besides the hanging habit and lack of latex, the specimens collected differ most distinctively from D. benguellensis Welw. on leaf arrangement, spiral versus horizontal; leaf shape subfalcate with an asymmetric base versus oblong, sub(ob)ovate, linear, elliptic, ovate and a symmetrical base; and peduncle length 0.1 cm versus (0.3)0.5–2.5(7) cm. The only specimen of D. benguellensis Welw. entered in the Global Plants database website collected close to a waterfall was M.G. Bingham 13204, but it did not resemble the specimens collected at the waterfall in the Luama Wildlife Reserve as its habit was erect and its leaves ovate.

D. benguellensis Welw. and the specimens collected from the Luama Wildlife Reserve are most conspicuously different in vegetative morphology, both in size and shapes. Key differences mentioned in the key to “succulent and semi-succulent species of the Old world” (Berg and Hijman 1999) distinguishes sister species mainly based on vegetative morphology, e.g. absent, short or long internodes; habit hanging, erect or ascending; root tuberous or rhizome at the base and or at internods; petiole short or long; number of lateral veins; length of the plant; and some ambiguous characteristics for some species such as absence or presence of stipules.

D. benguellensis has been characterized as highly variable, which might raise the question whether the specimens from the Luama Wildlife Reserve are an adaptation to growing on vertical rock faces. Are there two types of D. benguellensis Welw.? The most common one is erect and grows in between rocks and the hanging one is rare and only grows on vertical rock faces. If this were the case, than I would have expected to find the erect type at the same location of the hanging type. This was however, not the case.

Based on the differences in vegetative morphology, the specimens from the Luama Wildlife Reserve can easily be keyed out from the sister species in the same section of Kosaria (see the key provided under “distinct from other species”. These plants from the Luama Wildlife Reserve resemble ferns hanging from rocks. This has not been observed elsewhere for the genus. Therefore, I conclude that the specimens from the Luama Wildlife Reserve merit their own separate status as new species, Dorstenia luamensis M.E.Leal, sp. nov.

This study was financially supported by the Mac Arthur Foundation. The author is grateful to the Centre de Recherche en Sciences Naturelles (CRSN/Lwiro) for administrative support and to Phytokeys secretary for providing the essential references and the reviewers for their valuable comments.