Isolona heinsenii
Tree or shrub to 6(-12) m tall; d.b.h. to 10-15 cm; bark smooth, green-grey; branches spreading horizontally; young branches black, densely covered with short appressed hairs or rarely glabrous; old branches grey, sparsely covered with short appressed hairs to glabrous, striate. Petioles 3-5 mm long, 1-2 mm in diameter, densely covered with short appressed hairs or rarely glabrous, leaf lamina inserted on side, weakly grooved adaxially. Leaf lamina (8.5-)15-22 cm long, 3-8 cm wide, length:width ratio 2-3.5, narrowly obovate to obovate or narrowly elliptic to elliptic, papyraceous, glabrous to very sparsely covered with short appressed hairs abaxially, glabrous adaxially, dark green adaxially, light green abaxially, base broadly cuneate to rounded, apex acuminate, acumen ca. 1 cm long; midrib sparsely covered with short appressed hairs to glabrous adaxially, densely to sparsely covered with short appressed hairs or rarely glabrous abaxially; secondary veins 8-13 pairs, sparsely covered with short appressed hairs to glabrous on both sides. Rhipidia 1-2, on leafy branches. Flowering pedicels 5-12 mm long, ca. 2 mm in diameter, densely or rarely sparsely covered with short appressed hairs, light green. Lower bracts 1-3, ca. 1 mm long, ca. 0.5 mm wide, covered with short appressed hairs. Upper bract near the base of the pedicel or absent, ca. 0.5 mm long, ca. 0.5 mm wide, covered with short appressed hairs or rarely glabrous. Sepals 3-5 mm long, 2-3 mm wide, length:width ratio 1-2, narrowly to broadly triangular, base truncate, apex acute, densely covered with short appressed hairs or rarely sparsely covered with short appressed hairs, green, in mature flowers reflexed outwards, falling when in fruit. Corolla green when immature to light yellow with light red in center of tube at anthesis; tube 3-5 mm long, 4-6 mm in diameter, lobe:tube ratio 2.7-4.8, cupulate, covered with short appressed hairs or rarely glabrous outside, glabrous inside; lobes 15-19 mm long, 2-4 mm wide, length:width ratio 4.5-6.3, lorate to narrowly oblong, base truncate, apex round to acute, densely covered with short appressed hairs on the outside, less so on inside or rarely glabrous, coriaceous, spreading horizontally and then curving inwards, the margins folded outwards. Receptacle 4-5 mm in diameter. Stamens ca. 1 mm long; connective shield ca. 0.1 mm long, glabrous, light yellow, those of innermost whorl elongated and stretched against the ovary wall. Ovary 1-2 mm long, ca. 1 mm wide; stigma 3-4 mm, glabrous to sparsely covered with short erect hairs, light green. Fruiting pedicels 2-3 cm long, 3-4 mm in diameter, densely to sparsely covered with short erect hairs. Fruits 4-10 cm long, 1-3 cm in diameter, length:width ratio 3.6-4.5, narrowly ellipsoid, apiculate, apicule ca. 1 cm, 6-ribbed, glabrous, heavily speckled with white and yellow; pericarp ca. 3 mm thick. Seeds 15-20 mm long, ca. 10 mm in diameter, irregularly ellipsoid; testa smooth, light brown; hilum not seen.
Isolona heinsenii can be distinguished by the generally densely covered hairy leaves and flowers, larger sepals, petal lobes curving inwards over the receptacle and the conspicuously 6-ribbed fruits.
There are, however, a few specimens of I. heinsenii that are very sparsely hairy to completely glabrous on the leaves and young branches, and these seem to occur at lower altitudes (500-900 m). The floral parts are also glabrescent but are otherwise identical to those of the hairy specimens.
Molecular data strongly supports a sister relationship with I. linearis (Fig. 1). The latter species has many morphological differences from I. heinsenii (glabrous, fruits not ribbed). However, they do share the same habitat, both occurring in the montane rain forest of the Eastern Arc Mountains, with I. linearis mainly found in the South (Udzungwas) and I. heinsenii in the North (Usamabras), although some overlap does exist.
VU B2ab(iii). Isolona heinsenii is represented by a fair number of specimens in herbaria, and has been collected recently (2006). It can also be found in two protected areas: the Udzungwa National Park and the Amani Nature Reserve, both of which are in fairly good condition. However, it never grows in dense populations and can consequently become threatened because of its small Area of Occurrence (ca. 220 km2), which is why I apply the “vulnerable” category.
Eastern Tanzania, Eastern Arc Mountains; in montane rain forests, rarely in lowland rain forests; at (500-)1000-1440 m altitude.