Dorstenia luamensis (Moraceae), a new species from eastern Democratic Republic of Congo

Abstract A new species of Dorstenia L. (Moraceae), Dorstenia 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).


Introduction
In 2012, a specimen of Dorstenia L. was collected from the Luama Wildlife Reserve in eastern DRC (M.E. Leal 2551) hanging from vertical cliff s and rock faces close to a waterfall on the shear zone of two plateaus. Th ese plants have a typical Dorstenia L. infl orescence but their hanging habit and lack of latex is unusual. Th e only other hanging Dorstenia species (hemi-epiphyte) is D. astyanactis Aké Assi fi rst described from Ivory Coast (Ake Assi 1967) and later also collected in Cameroon (Pollard et al. 2003). Its infl orescence only has one appendix whereas the specimens from Luama have between 8 to12 appendices. Th e 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.
Th e 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). Th ey 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.
Th erefore in this study, I compared the specimens collected from the Luama Wildlife Reserve with D. benguellensis Welw. to determine: 1) whether diff erences are insignifi cant and the existing description of D. benguellensis Welw. should be broadened to incorporate these specimens, or 2) whether diff erences are signifi cant and these specimens should be described as a separate species. I argue that diff erences beyond habit are signifi cant and that they merit their own status as a new species from the Luama Wildlife Reserve, D. luamensis M.E.Leal.

Methods
Th e 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 signifi cantly diff erent from similar species within section Kosaria. Th e 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 diff er 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. Th e 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.

Discussion
D. benguellensis Welw. and the specimens collected from the Luama Wildlife Reserve are most conspicuously diff erent in vegetative morphology, both in size and shapes. Key diff erences 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.? Th e 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 fi nd the erect type at the same location of the hanging type. Th is was however, not the case.

Conclusion
Based on the diff erences 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". Th ese plants from the Luama Wildlife Reserve resemble ferns hanging from rocks. Th is has not been observed elsewhere for the genus. Th erefore, 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. Description. Lithophytes 10-17 cm long with a tuber 0.5 cm; stems aerial, hanging, glabrous; internodes 2.5-3 cm long; no white latex or translucent exu-date. Stipules absent or deciduous without scars. Leaves distichous; blade narrowly subfalcate 5-7 × 1-1.4 cm, membranaceous, apex micrunate, base cunate, adaxial side glabrous and subspiculate, abaxial side white and glabrous; margins entire;  petiole 1-2 mm long; venation brochidodromous; 5-7 pairs of secondary veins; tertiary veins scalariform. Receptacle elliptic to round, 3-4 mm in diameter, patelliform; margin greenish with triangular lobes (1 mm) and subspathulate appendages, 2-3 mm long; peduncle 1 mm long, glabrous. Staminate and pistilate fl owers (7 to 8) tightly packed in receptacle: perianth short lobed, whit apex minutely 2-3 lobed, glabrous; stigma 0.1 mm long. Drupes and seeds are unknown.

Dorstenia luamensis
Distinction from other species. Th is new species can be distinguished from any other Dorstenia species by its fernlike habit, hanging from vertical rock faces and the absence of latex.
Th e new species is added to the existing key of Berg and Hijman (1999) the "key to succulent and semi-succulent species of the Old World" Plants perennial, with rhizome or a tuber 5 Petiole relatively short, (0-)0.1-0. Distribution and conservation status. Th e species is distributed in small populations within the type locality, and according to these demographic characteristics it merits the conservation status of endangered (EN).
Etymology. Th e epithet luamensis refers the Luama Wildlife Reserve which is drained by the Luama River.