Euphorbia mbuinzauensis N. Wei, Mwachala, G.W. Hu & Q.F. Wang, 2021

Wei, Neng, Mutie, Fredrick Munyao, Mwachala, Geoffrey, Grace, Olwen M., Hu, Guang-Wan & Wang, Qing-Feng, 2021, Euphorbia mbuinzauensis, a new succulent species in Kenya from the Synadenium group in Euphorbia sect. Monadenium (Euphorbiaceae), PhytoKeys 183, pp. 21-35 : 21

Euphorbia mbuinzauensis N. Wei, Mwachala, G.W. Hu & Q.F. Wang sp. nov.

Figures 2 , 3

Type.

Kenya. Makueni County, Mbuinzau , 2°23'25.56"S, 37°54'42"E, 970 m, 29 Sep. 2018, Sino-Africa Joint Investigation Team (SAJIT) 007200 (holotype HIB!; isotypes EA!, HIB!, K!)

Diagnosis.

Euphorbia mbuinzauensis is most similar to E. pseudomollis , from which it differs by its shorter habit, up to 4 m (vs. to 9 m), abaxial leaves surfaces with densely stellate hairs (vs. simple hairs), 2- to 4-forked cymes (vs. 1- to 2-forked), bracts ca. 2.5 × 3.0 mm (vs. ca. 3.5 × 3.5 mm), dentate margin on bract (vs. entire or with a few teeth), cyathia 6 mm wide (vs. 8 mm wide), gland without narrow smooth margin (vs. with a narrow smooth margin), fruits ca. 8 × 7 mm (vs. ca. 10 × 10 mm), and ovoid seeds ca. 1.8 × 2.2 mm (vs. subglobose, ca. 2.5 × 2.5 mm).

Description.

Many-branched shrub to 4 m high. Branches cylindrical, fleshy, and marked with prominent elliptic leaf scars. Leaves fleshy, subsessile, deciduous at fruiting stage, with a pair of reduced stipules; lamina subrotund to obovate, to ca. 14 × 6 cm, apex rounded to obtuse with a recurved tip, margin slightly undulate, crenate, midrib distinctly keeled beneath, blade inflated, incurved, adaxial surfaces densely pubescent, green, turning to purplish grey green during dry season, abaxial surfaces densely stellate hairy, occasionally tinged purplish, with stellate hairs along the midrib. Inflorescences monoecious, in dense pseudo-umbels of 2-5 cymes on pubescent peduncles to 4 cm long; cymes 2-4-forked, with pubescent branches to 1.8 cm long; bracts subquadrate, ca. 2.5 × 3.0 mm, dentate, densely pubescent. Cyathia ca. 2.5 × 6.0 mm, with broadly funnel-shaped involucres, pubescent below; glandular rim ca. 1.2 mm wide, deeply furrowed and wrinkled, purplish red, mostly shallowly notched on the one side, but with a deep notch when young; lobes subquadrate, ca. 2.0 × 2.5 mm, purplish red, pubescent. Male flowers: staminate flowers 0.8 mm long, enclosed by involucral lobes and bracteoles; bracteoles fan-shaped, laciniate, plumose, 3 mm long, with pedicels minutely pubescent; pedicels 3 mm long. Female flowers: styles ca. 2 mm long, connate at the base, pubescent, with distinctly bifid thickened apices, deciduous in fruit. Capsules obovoid, deeply acutely lobed, apex depressed, to 8 × 7 mm, from purplish red to yellowish green, pubescent, explosively dehiscing septicidally and loculicidally into 3 2-valved cocci; pedicel recurved, pubescent, to 8 mm long; columella persistent, 6-7 mm long. Seeds ovoid, obscurely 4-angled, ca. 1.8 × 2.2 mm, pale brown to dark brown, shallowly tuberculate; caruncle rudimentary.

Distribution and ecology.

Only one population of the new species was found at the foot of Mbuinzau hill, Makueni County, Kenya (Figure 4 ). Here it grows in open deciduous woodlands covered by lava outcrops at an elevation of ca. 970 m.

Conservation status.

Only one population of the new species was found in an isolated woodland covered by lava outcrops (Figure 3A ) in Mbuinzau area. We assess the species as Endangered (criteria D1) according to the IUCN Red List Categories and Criteria ( IUCN 2001), due to the number of mature individuals (<250) in a very small and restricted population. Unfortunately, the habitat is threatened by human activities. For instance, its habitat has been fragmented by the Mombasa-Nairobi Railway and Mombasa-Road, which are the busiest traffic routes in Kenya. Moreover, the population is under threat from habitat loss, due to the exploitation of lava rocks in its habitat for construction.

Phenology.

Euphorbia mbuinzauensis was found with flowers in September and with fruits from September to December.

Etymology.

The epithet " Euphorbia mbuinzauensis " refers to its type locality, Mbuinzau in Makueni County, Kenya.

Notes.

The conspicuous latex is extremely poisonous to cattle as well as human beings, according to the comments from local farmers. We observed ants visiting the flowers and they are a possible pollinator to this species (Figure 3G ).

Additional specimens examined (Paratypes).

KENYA. Makueni County, Mbuinzau , 2°23'25.56"S, 37°54'42"E, elev. 970 m, 5 Dec. 2018, SAJIT 007411 (EA!, HIB!) .

Specimens examined for Euphorbia pseudomollis . Kenya. Makueni, Kibwezi, c. 1000 m, 2°26'S, 38°1'E, 22 Mar. 1906, G. Scheffler 137 (isotypes AMD [AMD.66883] image!, BM [BM000911307]!, K [K000238424]!, S [S13-12929] image!, WAG [WAG0004308] image!); Taita-Taveta, Mwatate , 3°31'S, 38°24'E, 29 Apr. 1963, P.R.O. Bally B12725 (BR [BR0000016225411] image!, K [K000238420]!) ; Taita-Taveta, Mwatate West of Voi , 3°30'S, 38°23'E, 15 Jul. 1960, L.C. Leach & R. Bayliss 10258 (K [K000238421]! & [K000238422]!) ; Kitui, Mutomo Hill Plant Sanctuary , 900-1000 m, 1°51'S, 38°13'E, 2 May 1970, J.B. Gillett 19141 (EA!, K [K000238423]!); Taita-Taveta , Taita, Sisal Estate, Senbi Hill , 1050 m, 3°31'S, 38°24'E, 17 Aug. 2000, P.A. Luke & W.R.Q. Luke 6432 (EA!) . Tanzania. Kilimanjaro, above Mwembe , 1005 m, 4°8'S, 37°51'E, 9 Apr. 1972, B.J. Harris BJH6342 (K [K000238425]!) ; Kilimanjaro, Mwembe , 4°10'S, 37°51'E, unknown date, P.R.O. Bally B11499 (E54) (K [K000238426]! & [K000238427]!) ; Dodoma, Mpwapwa , 1128 m, 6°21'S, 36°29'E, 30 Jun. 1938, Hornby 911 (K [K000238428]!) ; Tanga, Handeni, Kideleko , 609 m, 5°29'S, 38°1'E, 1 Jul. 1965, M.E. Archbold 471 (K [K000238430]!) ; Tanga, Handeni, Chanika Village , 700 m, 5°25'S, 38°1'E, 23 Sep. 1979, O. Hedberg et al. TMP194 (K [K000238431]!) ; Morogoro, Kilombero, Lugoda , 1800 m, 8°42'S, 35°49'E, Aug. 1988, E. Adiheysen 224 (K [K000238432]!) ; Iringa, a little north of Morogoro road, 1554 m, 7°30'S, 36°10'E, 27 Feb. 1962, R.M. Polhill & S. Paulo 1618 (BR [BR0000016225435] image!, EA!, K [K000238433]!, P [P00581481] image!) ; Lindi, 22 Apr. 1933, H.J.Schlieben n6383 (BR [BR0000016225428] image!) .

Specimens examined for Euphorbia bicompacta var. bicompacta : Kenya. Machakos, 1°31'S, 37°16'E, 7 Jun. 1902, T. Kassner 956 (Holotype K [K000237846]!; Isotype BM [BM000911306]!) ; Taita-Taveta, Wusi , 1371 m, 3°27'S, 38°21'E, May 1931, ERN 1322 (K [K000237843]!) ; Machakos, 1°31'S, 37°16'E, 27 Mar. 1940, P.R.O. Bally E144 (K [K000237845]!) ; Makueni, Kibwezi, Sisal Estate , 914 m, 2°26'S, 38°1'E, Jun. 1943, P.R.O. Bally B2573 (K [K000237847]!) ; Kitui, Migwani , 10 miles N of Migwani on Tharaka road, 0°57'18"S, 38°1'9"E, 3 May 1960, D.M. Napper 1596 (BR [BR0000016224810] image!, EA!, K [K000237848]!) ; Nairobi, Nairobi arboretum, 1768 m, 1°17'S, 36°49'E, Aug. 1932, I.R. Dale 2887 (K [K000237849]!) ; Nairobi, Langata , 1°20'S, 36°46'E, 20 March 1963, P.R.O. Bally B12659 (K [K000237850]!) ; Kiambu, Muguga , 1°11'S, 36°38'E, 8 Jun. 1962, J. Gichuru 14 (K [K000237851]!) ; Nyeri, Karatina , 0°29'S, 37°8'E, 24 Apr. 1943, P.R.O. Bally B2541 (EA!, K [K000237852]!) ; Embu, Thuchi, crossing on Embu-Meru road, 760 m, 0°25'S, 37°52'E, 4 Apr. 1970, J.B. Gillett & B. Mathew 19063 (BR [BR0000016224803] image!, K [K000237853]!) ; Laikipia, Kisima farm, 1700 m, 0°30'S, 36°30'E, 14 Jun. 1972, P.R.O. Bally B15106 (K [K000237854]!) ; Taita-Taveta, Msau River Valley , 800-950 m, 3°24'S, 38°24'E, 18 May 1985, C.H.S. Kabuye et al. 743 (K [K000237855]!) ; Taita-Taveta, Kasigau Mountain , 1000 m, 3°50'S, 38°40'E, 31 May 1998, W.R.Q. Luke et al. 5344 (K [K000237856]!) ; Elgeyo Marakwet, Arror lower, Pt 203, 1050 m, 1°0'55"S, 35°37'27"E, 30 Jul. 2017, Mwadime N 1861 (EA!) .

Figures

Figure 2. Euphorbia mbuinzauensis A flowering branch B leaf C the close-up of abaxial leaf to show densely stellate hairs D section through leaf to show the distinct keel on midrib beneath E cyathium, lateral view F cyathium, top view G dissected involucre to show lobes H male flower and bracteole I infructescence J fruit. K. Seeds. Scale bars: 2 mm (C-H, K); 1 cm (B, I, J). Voucher specimen: SAJIT 007200. Drawn by Nan Jia.

Figure 3. Morphological features of Euphorbia mbuinzauensis A habit B adaxial surface of leaf C abaxial surface of leaf D a branch with numerous infructescences E apical portion of flowering branch F, G Cyathium H seeds. Scale bars: 2 mm (F-H); 2 cm (B-E). Voucher specimens: SAJIT 007411 (A), SAJIT 007200 (B-H). Photo credit: Neng Wei.

Figure 4. Known distribution of Euphorbia mbuinzauensis in Kenya. The red dot indicates its only known locality.