Solanum agnewiorum Voronts., 2010

Vorontsova, Maria S., Kirika, Paul & Muthoka, Patrick, 2010, Overlooked diversity in African Solanum (Solanaceae): new and endangered Solanum agnewiorum from Kenya, Phytotaxa 10, pp. 31-37 : 32-36

Solanum agnewiorum Voronts. , sp. nov. ( Figs. 1 , 2b, 2c )

Solano anguivi similis sed aculeis uncinatis manifeste (nec rectis neque uncinatis), lobis folii acuminatis (nec rotundis neque acutis), inflorescentia flores 1–4 tantum (nec flores 5–22) ferenti, infructescentia baccas 1–2 tantum (nec baccas 5–22) ferenti, baccis 20-25 mm (nec 6–9 mm) diam, seminibus 5.5–6 mm (nec 1.8–2.5 mm) longis differt.

Type:— KENYA. Meru District: Igembe, Kangeta Division, Nyambene Forest , path from the forest office towards the first water reservoir, 0°13'57'' N, 37°53'27'' E, 2173m, 18 Apr 2010, Vorontsova, Ficinski, Kirika, Muthoka & Muroki 196 (holotype, EA; isotypes, BM, MO, K, NY) .

Perennial scrambler to 4m, heavily armed, moderately branched; young stems ascendant, sometimes tinged purple, sparsely stellate-pubescent; trichomes porrect, orange-translucent, sessile, the rays 6–8, 0.1– 0.15 mm, the midpoints elongated to 0.5–1 mm, reduced on some trichomes, with minute finger-hairs between the trichomes; prickles 1.5–3 mm long, 1–2.5 mm wide at widest point, always curved, brown, glabrous, spaced 2–5 mm apart; main branches 3–4 mm in diameter, glabrescent; bark smooth or with prickle scars, brown to red-brown. Sympodial units difoliate, geminate or not geminate. Leaves simple, the blades 6– 14 × 4.5–9 cm, ca. 2 times longer than wide, elliptic, membranous to chartaceous, drying concolorous to weakly discolorous, yellow-green to green-brown, sparsely stellate-pubescent on both sides; trichomes porrect, translucent, sessile, the rays ca. 8, 0.1–0.25 mm, the midpoints elongated to 0.3–1 mm, adaxially reduced with midpoints elongated to 1 mm, densely armed usually with over 20 straight prickles to 7 mm long protruding from primary to tertiary venation on both sides of the leaf; midvein raised abaxially, flat or raised adaxially, the primary veins 3–5 pairs, the tertiary venation visible on both sides of the leaf; base cuneate, often oblique; margin lobed, the lobes 2–5 on each side, 1–1.7 cm long, extending 1/4–1/3 of the distance to the midvein, deltoid, apically acuminate, the sinuses shallow, the terminal lobe longer than the rest; apex acuminate; petiole 1.2-6 cm, 1/4–1/2 of the leaf length, slender, weakly to moderately stellate-pubescent, with 2–10 straight or curved prickles, becoming straighter towards the apex. Inflorescences apparently lateral, 2–3 cm long, unbranched, with 1–4 flowers, with 1–2 flowers open at any one time; peduncle 0–5 mm long; rachis 0–0.8 cm long; peduncle and rachis sparsely stellate-pubescent, unarmed or with up to 5 curved prickles; pedicels 0.9–1.3 cm long, slender to stout, gently curved downwards, articulated less than 0.5 mm from base, moderately stellate-pubescent, with 0–5 fine straight prickles; pedicel scars small white stumps, spaced 2–7 mm apart. Plants andromonoecious, with 1–2 hermaphrodite flowers at the base and 0-2 staminate flowers at the apex of the inflorescence, the flowers all equal in size, 5-merous. Buds ovoid to ellipsoid. Calyx 3–4 mm long, divided for 1/4–1/3 of its length, the lobes 1–2 mm long, ca. 1.5 mm wide at base, deltoid, apically acuminate, unarmed or with up to 10 small straight prickles. Corolla 1.3–1.6 cm in diameter, white, opening flat, stellate, lobed for 2/3–3/4 of its length, the lobes 5–6.5 × 2.5–3.5 mm, deltoid, with a dark midvein, moderately stellate-pubescent abaxially, the trichomes porrect, irregular, orange-translucent, sessile, the rays 5–8, 0.1–0.2 mm, undulate, the midpoints shorter than the rays, lengthening towards corolla lobe apices, mostly glabrous adaxially, the trichomes variously reduced and irregular. Stamens with the filament tube ca. 1.5 mm; free portion of the filaments 0.4–0.6 mm; anthers 4–4.5 mm, free, equal, tapering, poricidal at the tips, the anther surface drying yellow to orange-brown, with occasional stellate trichomes, the pores lengthening into longitudinal slits with age, with a pronounced thick rim. ca. 0.7 mm in diameter, ovoid, glabrous, with a few stellate trichomes towards the apex; style 5.5–7.5 mm long on hermaphrodite flowers, brown, stout, straight, stellate-pubescent for most if its length, exserted 0.5–2 mm beyond the anthers, the vestigial style ca. 3 mm long on staminate flowers; stigma clavate, papillose. Fruit a globose berry, 1–2 per infructescence, 20–25 mm in diameter, spherical throughout development, the pericarp thin, smooth, shiny, glabrous, green with dark green stripes when young, dark yellow to yellow-orange at maturity, drying orange to brown or almost black; fruiting pedicels 2.5–3.5 cm long, 10–13 mm wide at base, woody, sometimes inflated towards the apex, pendulous, with 2–10 fine prickles; fruiting calyx not accrescent, covering less than 1/6 of the mature fruit, unarmed or with up to 10 small straight prickles. Seeds ca. 15–20 per berry, 5.5–6 × ca. 4.5 × ca. 0.8 mm, flattened-reniform, often somewhat irregular in outline, dull yellow-orange, the surface with raised outlines of cells or small pits ( Figs. 1 , 2b, 2c ).

Distribution and habitat:— Wet montane forest understorey in the Kenyan Central Highlands, 1800– 2500m elevation. Remnant forest patches near Limuru, the Aberdares, Mt Kenya east (Marimba forest), and Nyambene Hills. Croton –Brachylaena–Calodendrum forests near Limuru and Ocotea forests at Nyambene Hills and the Abardares (forest classification fide Beentje 1990, Figs. 2a , 3 ).

Etymology:— Named after Andrew and Shirley Agnew who first realised this was a distinct taxon and provisionally described it as “sp. J.”.

Additional specimens examined:— KENYA. Central Province. Kiambu District: Kangai Tea Estate , 1°05' S, 36°41' E, 2240m, 28 Jun 1987, Luke 445 ( EA) ; Limuru, adjacent to Limuru Girls High School , 1°07' S, 36°38'30'' E, 2286m, 26 Mar 1961, Polhill 363 ( EA) ; near Limuru Girls High School , 1°07' S, 36°38'30'' E, 2134m, 20 Aug 1961, Polhill 445, 455 ( EA) ; Limuru , 1°07' S, 36°38'30'' E, 2439m, Oct 1937, Van Someren 442 ( EA) ; Limuru , 1°07' S, 36°38'30'' E, 1981m, May 1945, Nattrass 348 ( EA) . Meru District: Kangeta Division, Nyambene Forest, a kilometre before arriving at the Nyambene main water intake, 0°22'49'' N, 38°28'20'' E, 1891m, 12 Mar 2003, Kimeu et al. KARI 11 /02 ( EA, K) ; Nyambene Forest , path to the left just after the entrance to forest, ca. 50 m after the entrance sign, 0°14'16'' N, 37°53'39'' E, 2097m, 17 Apr 2010, Vorontsova et al. 195 ( BM, EA, K, MO) ; Marimba Forest, NE Mt. Kenya , 0°02' N, 37°32' E, 2317m, 14 Oct 1960, Polhill & Verdcourt 2993 ( EA) . Nyeri District: Aberdare National Park , E side, 0°28' S, 36°54' E, 8 Apr 1975, Hepper & Field 4923 ( EA, P) .

Field observations:— Solanum agnewiorum is an easy to recognise species with distinctive acuminate leaf lobes, a dense covering of small curved prickles, and seeds significantly larger than those of any other African Solanum species. Occasional single-stemmed seedlings are seen on the dark forest floor (fig. 2b). Observations suggest that disperse populations of these non-reproductive seedlings are distributed throughout the forest understorey, and when a canopy gap appears they grow upwards attaching to other vegetation using prickles, developing into branched scramblers to 4 m tall and flowering.

Taxonomic placement:— Herbarium specimens of S. agnewiorum look deceptively similar to the common and hypervariable S. anguivi Lam. as its distinguishing characters in the fruit are easily overlooked due to scarcity of fruiting material. Most spiny Solanum shrubs from highland Africa with numerous flowers and fruits per inflorescence are part of S. anguivi Lam. Historically the majority of this species has been called “ Solanum indicum L.” and the epithet “ indicum ” was rejected ( Hepper 1978) due to historic confusion and widespread misapplication. Richard Lester’s group at the University of Birmingham have completed a multidisciplinary research programme on the species boundaries of this group and following his results we accept an inclusive concept of S. anguivi (for more information please see the treatment of S. anguivi published in Solanaceae Source, 2010 ). Solanum agnewiorum differs from S. anguivi by its prickles always curved (versus straight to curved in S. anguivi ), leaf lobes acuminate (versus rounded to acute in S. anguivi ), 1–4 flowers and 1–2 fruits per inflorescence (versus 5–22 flowers or fruits per inflorescence in S. anguivi ), fruits 20–25 mm diameter (versus 6–9 mm diameter in S. anguivi ), and seeds 5.5–6 mm diameter (versus 1.8– 2.5 mm diameter in S. anguivi ).

The habit and ecological niche of S. agnewiorum is more reminiscent of the Tanzanian endemic S. stipitatostellatum , another montane forest gap species scrambling up vegetation with its hooked prickles. Solanum stipitatostellatum has a dense covering of indumentum, entire to subentire leaves, and smaller fruits. Relationships in this group await clarification by molecular phylogenetic work currently in progress.

The collection Vorontsova et al. 196 has been chosen as the type because the duplicates are more broadly distributed than those of older collections, and include both flowering and fruiting material as well as field photographs.

Habitat decline:— The Central Highland soils are predominantly volcanic ( White 1983) and currently supporting a diversity of modern agricultural systems. Central Kenyan forests have been diminishing for several decades due to legal excision for settlement, agriculture, industry and exchanges ( Wass 1995). The following notes on forest decline in collection localities of S. agnewiorum have been compiled by Patrick Muthoka based on personal observations. The montane forest around Limuru and Limuru Girls High School no longer exists and no collections have made from that area since 1961. Most of the land in the Limuru and Tigoni areas is privately owned and divided for real estate development. The proximity of Limuru to Nairobi has contributed to rapid habitat destruction due to human migration. Marimba forest (part of Mt. Kenya east forest) is also under severe threat due to encroachment: the Kenyan government has cleared forest to develop the Nyayo tea plantations at the periphery of the closed forest at Marimba and Aberdare mountains, leading to an influx of workers. The only known stable population remains at the Nyambene forests that were gazetted in the 1980s ( Government of Kenya 1982), and where immediate threats to the species are not observed. The Aberdare forest collection locality was not visited for this survey.

Conservation status:— Endangered (EN) based in criteria B1(b) “Extent of occurrence estimated to be less than 5000 km 2, known to exist at no more than five locations, and continuing decline, observed, inferred or projected, in the extent of habitat” (IUCN 2010).

Seed conservation:— Seeds of S. agnewiorum are now conserved ex-situ at the National Gene Bank of Kenya, through the Kenya Seeds for Life Project supported by Kew Millennium Seed Bank partnership. Seed set for this species appears low and only a small number of seeds has been preserved.

Figures

FIGURE 1. Solanum agnewiorum (A–D drawn from Hepper & Field 4923; E, F drawn from Van Someren 422, by Lucy T. Smith). A. habit; B. abaxial surface of leaf with stellate trichomes; C. stellate trichome; D. flower; E. fruit; F. seed. Scale bar: A = 3 cm, B = 2.5 mm, C = 0.5 mm, D = 1 cm, E = 1 cm, F = 4 mm.

FIGURE 2. Solanum agnewiorum in its habitat (photographs A and B by Maria S. Vorontsova, C by Paweł Ficinski). A. path towards the main water intake in the Nyambene Forest, S. agnewiorum is commonly found on the sides of this path; B. seedling in the dark forest understorey; C. inflorescence with a short-styled flower; the hooked prickles attach to neighbouring vegetation as the plant scrambles upwards.

FIGURE 3. Collection localities of Solanum agnewiorum in Kenya.