Dorstenia christenhuszii M.W.Chase & M.F.Fay, 2013

Chase, Mark W., Thijs, Koen W., Kamau, Peris & Fay, Michael F., 2013, Dorstenia christenhuszii (Moraceae), a new species from the Taita Hills, Kenya, Phytotaxa 81 (2), pp. 45-48 : 46-48

Dorstenia christenhuszii M.W.Chase & M.F.Fay , sp. nov. ( Fig. 1 )

A species somewhat resembling the Tanzanian Dorstenia tenuiradiata Mildbraed (1934: 1065) , but differing in its glabrous stems (vs. puberulous) and inflorescence margins with all appendices filiform (vs. the inner ones triangular-linear); inflorescences usually tinged purple.

Type: ⎯ KENYA. K7 : Taita-Taveta District , Mbololo Hill, Mraru Ridge, primary forest along a stream with large boulders, 03˚19.916 ' S, 038˚27.078' E, 1630 m, 22 February 2012 , Christenhusz 6664, with P. Kamau , M. Mbale , J. Kyaa & M. W. Chase (holotype K!, isotypes EA!, H!) .

Fleshy herb to 80 cm. Stems succulent, ascending, rooting at the base, unbranched or sparsely branched, up to 1 cm thick at base, glabrous. Leaves spirally arranged, subsessile; petiole short, 0.5–3.0 cm, the blade attenuate to the 1 mm wide petiole wing; blade elliptic to obovate, 8.0–20.0 × 2.5–6.0 cm, bases attenuatecuneate, margins coarsely lobate-dentate in the upper half, usually with only one to a few lobes on each side, apices obtuse to acuminate; glabrous above, pubescent only on the midvein beneath, lateral veins in 5–7 pairs. Stipules subulate, caducous. Inflorescence, solitary, axillary; peduncle (1–) 4–5 cm, densely pubescent. Receptacle discoid becoming semi-globose, resembling a shuttlecock, flowering face circular, ca 1–2 cm. in diameter, margin up to 1.2 mm wide, appendages in two rows, the inner ones somewhat shorter than the outer ones, but all filiform in shape, up to 6 cm long, (usually) tinged purple. Staminate flowers spaced, perianth lobes 3; stamens 3, anthers two, white. Pistillate flowers spaced, numerous, with one green style. Pollinated by flies.

Other material examined: ⎯ KENYA. K 7: Taita-Taveta District, Mbololo Forest, 3°19'S, 38°27'E, forest on steep slopes, near forest stream, locally common, 1425–1850 m, 20 May 1985, Faden, Beentje, Ndegwa Ndiang’ui, Mutangah & Nyakundi 765 ( EA! US); Mbololo Forest, 3°19.58'S, 38°26.77'E, 1663 m, 27 March 2010, Kamau 457 ( EA!, H!); northwest of Mbololo forest, Kwambula water intake, Mrangi village, 3°32.538'S, 38°44.156'E, 1459 m, a weak herb to 40 cm high growing in a forest stream with Tabernaemontana stapfiana , Newtonia buchananii , Phoenix reclinata , Strombosia scheffleri , Craibia zimmermannii and Macaranga sp. , one population seen, 24 July 2009, Malombe & Matheka 1233 ( EA!); Mbololo forest, Kwambula water intake, 3°33.257'S, 38°44.669'E, 1558 m, a herb to 50 cm high, growing in a deep forest valley with Macaranga capensis , Strombosia scheffleri , Podocarpus falcatus, Pteris pteridioides and Coffea fadenii , rare species, 27 June 2011, Matheka and Miyawa 841 ( EA!); Mbololo forest, 0333 S / 38449 E, 1700 m, 18 August 2012, a herb to 80 cm high growing nearby a stream in a forest valley with Syzigium sclerophyllum , Newtonia buchananii , Strombosia scheffleri and Chrysophllum gorungosanum as dominant trees, Thijs, Steward, Keunen and Van de Peer ( EA!)

Conservation: ⎯The IUCN conservation pre-assessment for Dorstenia christenhuszii is EN B 1a (i, iii, v) + 2a (i, iii, v); C 2a (i); D. Full assessment will follow after publication of the species. Area of occupancy is estimated to be less than 500 km 2 in a forest facing fragmentation caused by increasing human populations. KT has also been in Chawia, Sagalla, Ndiwenyi, Kichuchenyi, Macha, Mwachora, Fururu and Ronge and only found D. brownii . The main current risk is the flammable, exotic plantations surrounding the indigenous forests. For instance, the Streptocarpus teitensis population was recently severely affected by fire.

Phenology: ⎯All specimens examined were fertile, and this species flowers throughout the year, both in the wild and in cultivation.

Distribution and ecology: ⎯Known only from Mbololo forest, ca 1550–1700 m. Mbololo hill is southwest-northeast oriented and crossed by a less pronounced south-north oriented ridge that divides Mbololo forest in four quadrants. The species only occurs near small streams in the valleys of the two southern quadrants. These locations (K. Thijs, unpubl. data) are characterized by a high canopy cover (mean ± SD: 77 ± 8%, n=5), shrub cover (37 ± 10%), litter cover (87 ± 7%) and leaf area index (4.0 ± 0.2 m ²/m²). The upper soil layer (0–10 cm) is characterized by soil acidity pH (H 2 O) (4.7 ± 0.7), soil conductivity (502 ± 265 µs/cm), total phosphorus (11.3 ± 8.2 MgP/kg), total nitrogen (0.5 ± 0.4 %) and total soil organic matter (3.1 ± 0.6 %). The most frequent tree species in the upper canopy layer (> 5m) are Strombosia scheffleri Engl. , Tabernaemontana stapfiana Britten , Macaranga capensis (Baill.) Sim , Craibia zimmermannia (Harms) Dunn and Newtonia buchananii (Baker) Gilb. & Bout. The understorey (<5m) is dominated by Garcinia volkensii Engl. , C. zimmermannia , Oxyanthus speciosus (K.Schum.) Bridson , Strychnos mitis S.Moore and Argomuellera macrophylla Pax. Tree regeneration is abundant for C. zimmermannia , Syzygium guineense F.White , N. buchananii , Xymalos monospora (Harv.) Warb. and Psychotria species.

Notes: ⎯Even though this species is locally abundant, growing among boulders in creeks on steep slopes, it is only known from three collections. From the same area, D. brownii has also been recorded: Faden 70/ 552, EA!, K!; Kamau 457, EA!, MO!. However, this species is caudiciform at maturity or with an underground tuber and otherwise clearly morphologically distinct; the two are not easily confused.

Etymology: ⎯The species epithet honours Dr Maarten J. M. Christenhusz (Founding Editor-in-Chief of Phytotaxa), who collected the type specimen and suspected that it was distinct from other East African Dorstenia species.

Cultivation: ⎯The species grows easily from seed and cuttings, but it requires high humidity and shade to thrive. It is currently in cultivation at the Helsinki Botanical Gardens, the Royal Botanic Gardens, Kew, and the University of Leuven.

Figures

FIGURE 1. Photographs of Dorstenia christenhuszii. Top left, habit of adult plant (by K. Thijs); top right, immature inflorescence and new leaf (by M. Christenhusz); middle, inflorescences at anthesis (both by K. Thijs); bottom left, insertion of peduncle (by M. Christenhusz); bottom right, detail of inflorescence with open flowers (by M. Christenhusz).