Rinorea calcicola Velzen & Wieringa, 2014

Rinorea calcicola Velzen & Wieringa View in CoL , sp. nov. ( Fig. 1 View FIGURE 1 )

Rinorea calcicola resembles Rinorea zenkeri with which species it shares the character of laminate fruits, but it has elliptic to obovate leaves and a thyrsoid inflorescence instead of obovate leaves with a racemose inflorescence.

Type   GoogleMaps :— GABON. Ogooué-Lolo: c. 4 km E of Lastoursville , old secondary forest next to limestone rockface, 0°48.25’ S, 12°45.92’ E, 330 m, 19 January 2008 (in fruit), J.J. Wieringa, P.H. Hoekstra, R. Niangadouma & J.-N. Boussiengui 5991 (holotype WAG! GoogleMaps ; isotypes LBV GoogleMaps , WAG! (2×) & 5 others to be distributed! GoogleMaps ).

Shrub up to about 2 m high; young branchlets pubescent. Cuspis/stipule 2–7 mm long, outer surface pubescent over the central area, margins ciliate. Leaves: petiole 6–12 mm long, 1.0– 1.8 mm in diameter, adpressed pubescent; blade elliptic to obovate, 7–30 × 3–10 cm, papyraceous–coriaceous, acuminate at apex, rounded to cuneate at base, glabrous but below with hairs in the axils of the secondary veins, glossy, dark green above, pale green beneath, margin shallowly serrate, bearing lignified teeth; midrib pubescent and prominent below, above with a narrow prominent ridge that is often flanked by parallel grooves (grooves only present when dried), both midrib and grooves sparsely pubescent; secondary veins 11–13 pairs, anastomosing 1–4 mm from the margin, glabrous to sparsely pubescent at base below. Inflorescence terminal, thyrsoid, c. 5 cm long, pubescent, budscale at base consisting of a reduced leaf with two reduced stipules, all three bearing an apical tooth; lateral branches decreasing in length towards the apex, basal ones up to c. 2 cm long, with up to c. 20 flowers; bracts triangular, decreasing in size to the apex of the inflorescence, c. 1–4 × 0.4–1.5 mm and topped with a tooth. Flowers zygomorphic, 4–5 × 3–4 mm, pedicel 1–1.5 mm long, pubescent; sepals triangular or ovate, 1.2 × 1.5–2 mm, sparsely pubescent with ciliate margins, pale greenish yellow with brown-red margin and apex, (1–)2–3(–4) with a (sub-)apical tooth; petals five, 3–4 mm long, pale yellow, often with a nail-like tooth at or just below the apex, posterior (adaxial) petals two, ovate, concave, rarely with a tooth, lateral petals two, ovate to bell shaped, usually with a tooth, anterior (abaxial) petal bell shaped, longitudinally folded, apex emarginate, inner surface hairy below the apex, outer surface with an often pubescent longitudinal ridge topped by a subapical tooth; androecium 3 mm long, staminal tube 1–1.5 mm long, up to 0.3 mm thick, glabrous, adaxially discontinuous except for a 0.1 mm high ridge and sometimes a velum connecting to the adaxial filament, margin regularly undulate; stamens diadelphous; adaxial filament ± free, c. 3 mm long, flattened, other 4 filaments inserted on the inner surface of the staminal tube, c. 2 mm long, flattened, anthers 1 mm long, connective scale red in dried flowers, ovate, c. 1 mm long, base decurrent on the upper half of the anthers, thecae with two ligulate connective appendages of c. 0.5 mm long; gynoecium flask-shaped, glabrous, ovary part developing black cork spots, style extending just beyond the connective appendices, ovary 1-loculate, with c. 6 ovules, placentation parietal. Fruit a capsule, obovoid-triangular, c. 13–17 × 9–12 mm, surface with lamellate corky protrusions of 1–3 mm long, up to 6-seeded; seeds tetrahedric, acutely angled, 5–6 mm long, smooth, grey or brown, dorsal faces concave, inner faces flat or concave.

Distribution: —SE Gabon, upper Ogooué River ( Fig. 2 View FIGURE 2 ).

Habitat & Ecology: —Old secondary forest along the upper Ogooué River, 250–420 m elevation, on limestone (see discussion). Flowers observed in September, buds in December, fruits in December and January.

Etymology: —The epithet calcicola , meaning “living on chalk”, refers to its assumed association with limestone (see below).

Conservation: —We assess Rinorea calcicola as Endangered, EN B1ab(ii,iii,iv,v), according to IUCN standards ( IUCN 2001) and want to emphasise that further research may result in a status of Critically Endangered (CR). At present, R. calcicola is only known from three collections, with two localities being fairly close together (13 km apart) that we consider to belong to the same population. Three localities are just enough to calculate both an EOO and an AOO. The EOO of 884 km 2 falls within the Endangered range, while the AOO (cell size 14 × 14 km) of 616 km 2 indicates Vulnerable. We have used the sliding scale for grid cell size because we consider the 2 × 2 km grid cell size as advocated by IUCN in general far too small for botanical data from areas with relatively low sampling like Gabon. A grid cell size of 2 × 2 km would have resulted in a AOO of 12 km 2, being only slightly above the limit for Critically Endangered (CR). However, if we assume this species to be restricted to limestone, its actual AOO might be even less than 1 km 2, because the total amount of limestone in south-eastern Gabon is very limited ( Delorme 1979). One of the two known populations, that of Lastoursville, is under serious threat from local agriculture; when Wieringa et al. 5991 was collected in 2008, slash-and-burn cropping fields were less than 100 metres away, while the label of Breteler & de Wilde 785 from 1978 reads “Forest edge bordering local plantation”. Other parts of the limestone strip may be a little further away from the agriculture front, but the species is only present in patches and does not occupy the full limestone strip. The locality SE of Franceville does not seem to be under any specific threat at the moment. Further research should establish whether the species is present on other limestone outcrops in the region.

Notes: —The most characteristic feature of Rinorea calcicola is the lamellate fruit. This character is shared only with R. zenkeri , which is a Cameroon endemic restricted to semi-deciduous forests ( Achoundong 1996). Whereas R. zenkeri has obovate leaves with a cordate base and a racemose inflorescence, R. calcicola has elliptic to obovate leaves with an obtuse to cuneate base and a thyrsoid inflorescence. Another morphological peculiarity of R. calcicola is the strict diadelphous stamen arrangement. Whilst other Rinorea species with well-developed staminal tubes may have some free stamens, they are never as consistently diadelphous as those of R. calcicola . We initially selected Breteler & de Wilde 785, previously identified as R. cf. dentata, as possibly conspecific with the type collection (Wieringa et al. 5991) based on the shared character of relatively dense pubescence on the underside of the leaf midrib. On closer examination, the staminal tube morphology appeared to be different from that of R. dentata confirming that Breteler & de Wilde 785 did not represent that species. Taking into consideration the vegetative similarities of Breteler & de Wilde 785 with the two other collections of R. calcicola and the proximity of the collection locality to Wieringa et al. 5991, we concluded that all three collections represent the same taxon. This is further corroborated by one ovary of Breteler & de Wilde 785 which has dark spots which we interpret as developing cork lamellae. Also, the very young buds of de Wilde et. al. 9923 compare well with the flowers of Breteler & de Wilde 785, although the staminal tube is not yet developed and the young petals have more pronounced teeth than those of open flowers. As conspecific status of the fruiting and flowering material described here cannot be fully confirmed due to the lack of available fully developed flowers and fruits on the same individual, we have decided to designate Wieringa et al. 5991 as the type collection, in contrast to the traditional type assignment of flowering material.

Additional material examined (paratypes): — GABON. Haut-Ogooué: falls in the Djoumou River, c. 7 km SE of Franceville on the road to Ndoumou , secondary high forest, ± 350–420 m, 1°41’ S, 13°40’ E, 6 December 1989 (in fruit and young floral buds), J.J.F.E. de Wilde et al. 9923 ( WAG!, LBV, 6 duplicates to be distributed!) GoogleMaps ; Ogooué-Lolo: c. 10 km along the road from Lastoursville to Mékouyi , forest edge bordering local plantation, ± 250 m, 0°52’S 12°40’E, 25 September 1978 (in flower), F.J. Breteler & J.J.F.E. de Wilde 785 ( BR, C, LBV, MO, P, WAG!) GoogleMaps .