Pauridiantha chlorantha (K.Schum.), 2019

Salvator NTORE & Olivier LACHENAUD, 2019, Two new species and a new combination in the genus Pauridiantha Hook. f. (Rubiaceae) from tropical Africa, Adansonia 41 (4), pp. 29-40 : 32-34

Pauridiantha chlorantha (K.Schum.)

Ntore & O.Lachenaud, comb. nov.

Urophyllum chloranthum K.Schum., Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie 28: 57 (1899). — Rhipidantha chlorantha (K.Schum.) Bremek., Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie 71: 222 (1940). — Typus: Tanzania. Uluguru Mts, Ngamba , 19.X.1894, Stuhlmann 8883 (holo-, B, delet. ). — Neotypus: Tanzania. Uluguru Mountains, 15.XI.1967, Harris, Hedberg & Mwasumbi 1148 (neo-, EA [ EA000065027 !], here designated; isoneo-, BR[BR0000017774529!], K!).

DISTRIBUTION. — Zanzibar-Inhambane regional mosaic. Endemic to the Uluguru Mts in central-eastern Tanzania ( Fig. 2 ).

HABITAT. — Montane evergreen forest, 1400-1845 m in elevation.

PHENOLOGY. — Flowers from September to December (young inflorescences in August); fruits in November-December (immature), January (almost mature), March and May (immature).

PRELIMINARY CONSERVATION ASSESSMENT. — Endangered [EN B1a b(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v)]. Pauridiantha chlorantha , comb. nov. was previously assessed by Lovett & Clarke (1998) as Vulnerable B1+2b, D2, but this appears to be an underestimation of its threat status. Its extent of occurrence (EOO) is calculated to be 75 km ², and its area of occupancy is estimated to be 36 km ², which fall respectively within the limits for Critically Endangered under subcriterion B1 and Endangered under sub-criterion B2. The species is endemic to the Uluguru Mountains in Tanzania, where it grows in submontane forest between 1400 and 1845 m in elevation. It is known from 15 herbarium specimens collected between 1914 and 2009, representing two subpopulations, around 15 km apart. Although its range lies within a protected area (Uluguru Nature Forest Reserve, declared in 2009), its habitat is under serious threat from agriculture, logging, firewood collection, and invasive exotic species ( Rubus and Maesopsis ) ( Burgess et al. 2002). A third subpopulation (not taken into account in EOO and AOO calculations), at c. 7°05’S, 37°25’E, is now probably extinct due to deforestation, no suitable habitat being left in the area according to GoogleEarth images. A decline in EOO, AOO, habitat extent and quality, number of subpopulations, and number of individuals is therefore obvious. The two subpopulations represent two ‘locations’ (sensu IUCN 2012) and the species qualifies for Endangered status according to the conditions B1ab(i,ii,iii,i v,v)+2ab(i,ii,iii,iv,v).

AFFINITIES. — Pauridiantha chlorantha , comb. nov. is similar to P. insularis (Hiern) Bremek. and P. principensis Ntore & O.Lachenaud , sp. nov., both from the Gulf of Guinea islands; the similarities and differences between them are discussed under P. principensis , sp. nov. below.

OTHER MATERIAL STUDIED. — Tanzania. Uluguru Mts, Bondwa-Lupanga col, 6°54’S, 37°42’E, 1.V.1970, Harris & Pócs 4543 ( EA [ EA000065025 !], K [ K000352753 !)]; Mwere Valley (Bondwa / Mwere col), Uluguru Mts , 26.IX.1970, Harris, Pócs, Faden & Csontos 5124 ( EA [ EA000065028 !], K [ K000352750 !, K000352756 !]); Uluguru North Catchment F.R., on the path Tegetero-Luhungo, just W of the ridge from Bondwa Peak to Nziwane , 14.I.2001, Jannerup & Mhoro 129 ( K); ibid., Jannerup & Mhoro 135 ( K); North Uluguru F. R., 8.XII.1993, Kisena 2123 ( K [ K000352755 !]); Ng’ubabule, North Uluguru F.R ., 9.XII.1993, Kisena 2124 ( BR [ BR0000009210059 !], K!); Lupanga Peak , 6°52’S, 37°42.5’E, 28.VIII.1981, Lovett 212 ( K [ K000352752 !]); Uluguru North Forest Reserve, permanent sample plot 1 (near Mwele River ), 6°54’09”S, 37°41’03”E, 1640 m, 15.X.2009, Mwangoka, Shirima, Hamisi, Swai, John, Seki & Kasimu 6409 ( MO [ MO-3025815 ]); Uluguru Mts , Bunduki Forest Reserve , III.1953, Paulo 52 ( EA [ EA000065029 !], K [ K000352759 !]); Uluguru, Urwald sudöstl. van Mission Schlesien uber Morogoro , 1.XI.1914, Peter 52120 ( BR [ BR0000017774536 !], K [ K00352754 !]); N-Uluguru Mts, E slopes of Lupanga, 10.X.1971, Pócs & Mwanjabe 6469/B ( EA [ EA000065588 !]); N-Uluguru Mts, N slope of Bondwa near the springs, 24.X.1972, Pócs 6804B ( EA [ EA000065026 !]); Morogoro District , 3600ft; 25.XI.1932, Wallace 490 ( K [ K000352751 !, K000352757 !, K000352758 !]) .

DESCRIPTION

Shrub

2-4 m tall; twigs cylindrical or slightly 4-sulcate, 1.5-5 mm thick, glabrous or minutely puberulous just above the nodes.

Stipules

Rather soon caducous and leaving corky scars, triangular, 3.5-9 × 1.5-3 mm, thickened with margins recurved inwards, narrower than the twig, glabrous or very sparsely puberulous.

Leaves

Petiole. 0.6-2.3 cm long, with very sparse short appressed hairs;

Leaf-blade. Elliptic to obovate, 8.5-23 × 2.5-12 cm, cuneate at base, abruptly acuminate at apex with acumen 0.8-2 cm long, coriaceous, sparsely appressed-puberulous on both sides when very young, soon becoming glabrous (or sometimes with very sparse hairs persistent on the underside of the main veins), drying olive green to olive brown; midrib flat or faintly impressed above; secondary veins (10-)12-15 pairs, weakly to moderately ascending, forming conspicuous loops 0.5-5 mm from the margin; tertiary veins prominently reticulate below, forming areolae <0.5 mm in diameter.

Domatia. Present as glabrous pits in primary and secondary vein axils.

Inflorescences

Axillary, 1-3 in each axil, laxly cymose, 3-8-flowered, 1-2.5 cm long, minutely and sparsely pubescent.

Peduncle. 0.5-1.5 cm long, with a pair of stipulate prophylls c. 2.5 × 0.5 mm inserted between ¼ and ½ of its length from the base.

Floral bracts. Absent.

Flowers

5-merous.

Pedicel. 1.5-4 mm long, slender, shortly and sparsely pubescent.

Calyx. Cupuliform, entirely glabrous or sparsely pubescent outside, with a tube 0.2-0.5 mm high and minute triangular lobes 0.2-0.5 mm long, lacking colleters.

Corolla. White or pale green, with cylindrical to campanulate tube 1.7-2(-3) × 1.2-2.3 mm, glabrous outside, densely villose inside at the throat, and triangular lobes 1-1.5(-2.3) × 0.7-1(-1.5) mm, glabrous outside, papillate inside.

Floral bud. With cylindrical base and ellipsoid, obtuse apex.

Stamens. Fully exserted with filaments c. 1 mm long in brevistylous flowers,half-exserted and subsessile in longistylous flowers,anthers elliptic, c. 0.7 × 0.3 mm (including minute sterile appendage).

Disk. Hemispherical, c. 0.5 mm high, ± grooved, minutely papillose.

Ovary. (4-)5-locular below, (8-)10-locular by false septa in the upper part, c. 1 mm high, sparsely puberulous.

Style. Included, c. 0.8 mm long including the 5-lobed stigma c. 0.5 mm long, glabrous at base and papillose at apex in brevistylous flowers, or exserted, c. 2.3 mm long including the 5-lobed stigma c. 0.3 mm long, glabrous at base and villose at apex (the exserted portion) in longistylous flowers.

Fruits

Broader than long, 2-3 × 3-4 mm, glabrous, crowned with persistent calyx slightly accrescent in width, 1.5-2 mm wide; pedicels slightly accrescent in the fruiting stage, 4-6 mm long.

Seeds

Numerous, ellipsoid, c. 0.5-0.55 × 0.45 mm.

Exotesta cells

Polygonal with strongly raised margins, forming a conspicuous reticulum; radial walls thickened with small pits; inner tangential wall thickened, with large pits ( Fig. 1A, B ).

REMARKS

For an illustration of this species see Verdcourt (1976: fig. 15). The type collection has presumably been destroyed during the Second World War, and no duplicates have been traced. Later collections from the same area are certainly conspecific (no similar species being found in the region) although some details of the protologue do not agree with them ( Verdcourt 1976). In particular, Schumann described the calyx as 1.5 mm long and the corolla tube as 5 mm long (both measurements apparently somewhat exaggerated) and the petiole as 1-2 mm long (presumably a slip for 1-2 cm). He also described the anthers as included, and the gynoecium as consisting of 5 very short free styles 0.6 mm long. The material we have seen actually shows two distinct flower morphs, none of which completely fits this description:brevistylous flowers have a short style divided nearly to the base – thus more or less as described by Schumann – but exserted anthers, while longistylous flowers have partly included anthers but a long exserted style divided only at the apex. Schumann’s description of the style and anthers may therefore have been based on a flower in bud. Among the extant collections, Harris et al. 1148 was chosen as neotype since it is a good flowering specimen and is represented in several herbaria.

The description of the species by Verdcourt (1976) is incomplete as regards the heterostyly, the domatia (not mentioned) and the fruits and seeds, unknown then and described here for the first time. The maximum height of 15 m tall, mentioned by Verdcourt, seems very dubious: all collections seen by us are reported as shrubs 2-4 m high.

Figures

FIG. 2. — Distribution map of Pauridiantha chlorantha (K.Schum.) Ntore & O.Lachenaud, comb. nov.

FIG. 1. — Seeds of Pauridiantha chlorantha (K.Schum.) Ntore & O.Lachenaud, comb. nov., from Jannerup & Mhoro 129 (A, B) and P. gracilipes O.Lachenaud & Ntore, sp. nov., from Lachenaud et al. 1981 (C, D) in electron microscopy: A, C, entire seed; B, detail of exotesta cells with outer tangential wall removed, showing thickened radial walls with small pits, and large pits in the inner tangential walls; D, detail of exotesta cells with outer tangential wall removed, showing thin radial walls with small pits, and large pits in the inner tangential walls. Scale bars: A, C, 100 µm; B, D, 10 µm.