Greenwayodendron usambaricum (Verdc.) Lissambou, Hardy & Couvreur, 2018

Lissambou, Brandet-Junior, Hardy, Olivier J., Atteke, Christiane, Stevart, Tariq, Dauby, Gilles, Mbatchi, Bertrand, Sonke, Bonaventure & Couvreur, Thomas L. P., 2018, Taxonomic revision of the African genus Greenwayodendron (Annonaceae), PhytoKeys 114, pp. 55-93 : 55

Greenwayodendron usambaricum (Verdc.) Lissambou, Hardy & Couvreur comb. nov.

Greenwayodendron suaveolens subsp. usambaricum Verdc., Adansonia, sér. 2, 91. (1969).

Type.

TANZANIA. Tanga: Kwamkoro to Potwe. E. Usambaras, Dec 1936, P.J. Greenway 4810 (lectotype, designated by Verdcourt 1969 p. 69, K![K000580892]; isotypes K![K000580893], EA).

Tree 12-30 m tall, d.b.h not observed. Young branches at first sparsely pubescent, later glabrous, trichomes 0.1-0.8 mm long, erect; old branches glabrous. Leaves: petiole 4.5-6.0 mm long, 1.5-2.1 mm in diameter, densely to sparsely pubescent, trichomes 0.1-0.8 mm long, indumenta brown; lamina 11.2-16.5 cm long, 4.1-6.4 cm wide; length:width ratio 2.3-3.0; elliptic to narrowly elliptic, base rounded or cuneate, apex acuminate, apiculate, acumen 10-25 mm long, upper side glabrous, lower side densely pubescent to sparsely pubescent; midrib upper side basely sparsely pubescent, lower side densely to sparsely pubescent, trichomes 0.3-0.7 mm long; secondary veins 14-18 pairs, upper side glabrous, lower side pubescent to sparsely pubescent, trichomes 0.3-0.8 mm long; tertiary veins irregularly prominent, slightly raised or indistinct above. Floral buds ellipsoid, 6-9 mm long, 2.0-3.2 mm in diameter, densely pubescent. Flowers not observed. Fruiting pedicel 12-13 mm long, 2.0-2.5 mm wide, sparsely pubescent, trichomes 0.4-0.5 mm long; stipes 5.5-6.5 mm long and 1.0-1.2 mm wide, sparsely pubescent; monocarps 2-4, 11.6-12.2 mm in diameter, broadly ellipsoid to globose, sparsely pubescent to glabrous, green turning wine red at maturity; seeds 1-2 per monocarp, 11.0-11.2 mm in diameter, ellipsoid to globose, flattened on one side when more than one seed per monocarp, surface covered by a white tegument.

Distribution.

Only known from northern Tanzania, in the East Usambara Mountains, 320-1124 m (Fig. 12 ).

Habitat and ecology.

Mature forest in mid-altitude mountain.

Phenology.

Flowering and fruiting are not well known. Nevertheless, floral buds samples were collected in November and December. Fruit specimens were collected from August to November.

Vernacular names.

Unknown.

Uses.

Unknown.

Preliminary IUCN conservation status.

Vulnerable [VU]. The extent of occurrence (EOO) of Greenwayodendron usambaricum is estimated to be over 2 km2 (within the 20,000 km2 upper limit for Endangered status under criterion B1) whereas its minimal area of occupancy (AOO) is estimated to be 36 km2 which falls within the limits for Endangered status under criterion B2. Greenwayodendron usambaricum is endemic to the Usambara Mountains in Tanzania where it is dominated under canopy. It has been collected in one protected area (Mount Usambara). This species is known from 9 specimens representing 7 subpopulations. These 7 subpopulations represent a total of 7 “locations” (sensu IUCN 2012), exceeding the upper limit for Endangered status, but falling within the limit for Vulnerable status. The main G. usambaricum threat is habitat destruction resulting from logging and intensive agriculture in Tanzania. We project that the ongoing loss of its habitat will induce a strong continuous decline in the number of subpopulations and mature individuals in the next ten years as well as an important decline of its EOO and AOO. Greenwayodendron usambaricum is therefore assigned a preliminary status of VU B1ab(i,ii,iii,iv,v) + B2ab(i,ii,iii,iv,v).

Notes.

Initially, individuals from the Usambara Mountains in Tanzania were considered part of G. oliveri . Indeed, Engler and Diels (1901) cited the specimen Scheffler 74 (Usambaras) under Polylathia oliveri . Verdcourt (1969) then described the Usambara specimens as a subspecies of G. suaveolens , recognising little morphological differentiation with G. suaveolens . Here, we consider these individuals as representing a separate species from G. suaveolens . Indeed, besides its disjunct and isolated distribution, G. usambaricum can be distinguished from G. suaveolens by the higher number of secondary veins (≥ 14 versus ≤ 12 for G. suaveolens ). Nevertheless, more flowering material is needed to better understand the morphological differences between these two species. These observations are corroborated to a certain extent by population genetic data such as microsatellites (Lissambou et al. in prep.) and especially nuclear phylogenetic analyses of the genus (Couvreur et al. in prep.). In the latter case, G. usambaricum was reconstructed as sister with maximum support to a clade containing G. gabonicum , G. glabrum , G. litorale and G. suaveolens .

Specimens examined.

Tanzania. Tanga: Bomole, Amani, hill trail ca. halfway to summit in area of natural forest, 5°02'S, 39°10'E, 4 Jun 1996, Johnson, D.M. 1943. Bomole, Amani Nature Reserve. East Usambara Mountains. Mature forest, 4°55'S, 38°36'E, 10 Oct 2007, Marshall, A.R. 1260 (K); Bomole, Amani Nature Reserve. East Usambara Mountains, 4°55'S, 38°36'E, 8 Aug 2007, Marshall, A.R. 1094 (K). Usambara, Afrika, Landsaft, 4°42'S, 38°21'E, 29 Aug 1916, Peter, A. 17595 (K, WAG); Usambara, Afrika, Landsaft, 4°42'S, 38°21'E, 29 Aug 1916, Peter, A. 18130 (K, WAG); Tanga. Kwamkoro, 4°42'S, 38°21'E, 11 Jun 1986, Ruffo, A. 2195 (K); Tanga. Kwamkoro F.R, 4°42'S, 38°21'E, 4 Aug 1961, Sensé, SR. 3238 (BR).

Figures

Figure 12. Distribution of Greenwayodendron usambaricum.