Sabicea arborea K. Schumann (1899: 58)

Zemagho, Lise A., Liede-Schumann, Sigrid, Lachenaud, Olivier, Dessein, Steven & Sonke, Bonaventure, 2017, Taxonomic revision of Sabicea subgenus Anisophyllae (Ixoroideae, Rubiaceae) from Tropical Africa, with four new species, Phytotaxa 293 (1), pp. 448-450 : 448-450

1. Sabicea arborea K. Schumann (1899: 58) Pseudosabicea arborea (K. Schumann) N. Hallé (1964: 397) . Type:— TANZANIA. Uluguru Mts., Ngluwenu, 1500–1700 m, 18 November 1894, Stuhlmann 8775 (holotype B†). Neotype

(designated by Hallé 1964: 398):— Tanzania, bezirk Morogoro: Uluguru-Gebirge, Nordwestseite, Lupanga , 2100 m , 12

November 1932, H.J. Schlieben 2970 (neotype BR [ BR0000008851536 ]!, isoneotypes GH, P [P03793473]!) .

Woody vine or shrub (probably sarmentose); stems up to 2 m long, 1–3 mm thick, densely white-felted in the young stage, later glabrescent. Leaves opposite, equal in size; petioles 0.5–1 cm long, densely white-felted and sometimes also with stiff hairs on the upper side; blades elliptic, 3.9–8 x 1.8–3.3 cm, symmetrical, acute or obtuse at base, acuminate at apex, coriaceous, strongly discolorous; upper side green, in the young stage sparsely felted, soon becoming glabrous; lower side buff to whitish, densely felted with woolly hairs; secondary veins 10–15 on each side of midrib. Stipules opposite, free and interpetiolar, ovate, 5.5–6 x 4–4.5 mm, entire, acute or obtuse at apex, erect or reflexed, glabrous or sparsely felted on both surfaces, and inside with ca. 1 mm long silky hairs at base. Inflorescences axillary on leafy portion of stems, 1 (–2) per node, sessile, densely glomerulate, many-flowered, 1.2–1.8 cm in diameter. Bracts free, not clearly surrounding the inflorescence, ovate, 7–7.5 x 3–4 mm, entire and acute at apex, slightly concave, sparsely white-felted outside, glabrous inside, the base with long silky hairs on both surfaces; bracteoles narrowly ovate to narrowly triangular, 2–5 x 0.7–1.5 mm, with indumentum similar to the bracts. Flower buds nearly cylindrical, slightly enlarged at apex. Flowers 5-merous, sessile. Hypanthium densely white-felted, with stiff hairs ca. 1 mm long near the base. Calyx tube cylindrical, ca. 1.2 mm long, lobes triangular, 0.5–1.5 mm long, erect, densely white-felted outside, densely villose inside with silky antrorse hairs ca. 1 mm long. Corolla white; tube cylindrical, 4–6 x 1.2 mm, lobes narrowly elliptic, 2–3.5 x 1–1.2 mm; corolla densely felted with short woolly hairs outside, apex lobes sometimes also with silky hairs ca. 1.5 mm long; upper portion of tube sparsely pubescent inside, with hairs ca. 0.4 mm long. Stamens either included,

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subsessile and attached in the upper part of the tube with their apex almost reaching mouth in long-styled flowers, or fully exserted on very short filaments in short-styled flowers; anthers ca. 1.5 x 0.3 mm. Disk cylindrical, ca. 0.3 mm long, glabrous. Style glabrous, 5 mm long, just reaching corolla mouth in long-styled flowers, or ca. 4 mm long and included in short-styled flowers; stigmatic lobes 1–1.5 mm long, narrowly cylindrical. Fruits and seeds unknown.

Distribution: —Afromontane Region. Sabicea arborea is endemic to the Eastern Arc Mountains of Tanzania, occuring in the Uluguru, Nguru and Udzungwa ranges ( Fig. 8 ).

of the species are in bold.

TAXONOMIC REVISION OF SABICEA SUBGENUS ANISOPHYLLAE

Phytotaxa 293 (1) © 2017 Magnolia Press • 17

Habitat and ecology: —This species grows in montane rain forest, at 1600–2200 m altitude.

Phenology: —Flowering from November to February.

Discussion: — Sabicea arborea is most similar to S. bequaertii and S. tersifolia , both of which were previously considered conspecific by Hallé (1964) and Verdcourt & Bridson (1988), but we consider them to be sufficiently different to be recognised as a distinct species. Sabicea becquetii is also similar to this group; the differences between these four species are summarised in Table 2.

Notes: —The habit of S. arborea , which is variously described as a shrub, climber or scrambling herb, needs further study in the field (see also the discussion of morphological characters in the group). It was originally described as a tree, but this is evidently erroneous.

A collection from the Udzungwa Mountains in Tanzania, Luke et al. 6904 (BR, K), closely resembles S. arborea , but differs by the presence of long stiff hairs on the stems and both sides of the leaves (in addition to short woolly hairs); and the bracts are also slightly larger. This specimen unfortunately lacks flowers. Better material is needed to decide its status; it is likely to represent a new taxon.

Conservation status:— IUCN Red List Category: Endangered [EN B2ab(i,ii,iii,iv,v)]. The extent of occurrence is estimated as 11,975.224 km 2, and the area of occupancy as 12 km 2. The first value falls within the limit for Vulnerable under criterion B1 (although the EOO is not a very relevant criterion for a montane species with disjunct range) and the second is below the threshold for Endangered under criterion B2. The species is known from only three locations (sensu IUCN 2012). The Eastern Arc mountain forests of Tanzania, where it occurs, are threatened by deforestation for agriculture and charcoal production, so a decline in the extent of occurrence, area of occupancy, extent and quality of habitat, number of locations and number of individuals can be predicted.

Additional specimens examined:— TANZANIA. Morningside to Bondua Peak, Uluguru Mts above Morogoro, montane rain forest on the W slope of Mt. Palata , 1600–1800 m, 28 February 1982, A. Borhidi et al. [co-collectors unknown] 82262 ( MO, UPS); Uluguru, Bunduki, 27 January 1935, E.A. Bruce 668 (K, MO); Uluguru Mountains , 26 December 1931, B.D. Burtt 3472 (K); Uluguru Mountains , 22 January 1976, P.J. Cribb & C. Grey-Wilson 10351 (K); Kawemba F.R., 8 December 1995, C. Kisena & C. Mmari 1655 (K); Nguru Mts , above Divue headwater, 6 km SSE Maskati Mission, 12 February 1991, S. Manktelow, T. Pocs & U. Svenson 91347 ( BR, K, MO, UPS); summit of Lupanga, Uluguru Mountains , 23 December 1933, A.P.G. Michelmore 854 (K) .

Figures

FIGURE 8. Distribution of Sabicea arborea, S. aurifodinae and S. becquetii.