Prionostemma
Description
Lianas or shrubs; bark with red juice; branches (sub)opposite or alternate, branchlets often scabrouswith sparse, rigid, short hairs, angled and subterete, almost at right angles with the main branch. Leaves scabrous. Petioles glabrescent, sparsely scabrous. Inflorescences axillary towards the apex of branches, paniculate or pseudo-cymose, pedunculate, scabrous, tomentose. Flowers tomentellous, rather large for the family; calyx campanulate, glabrescent with 5 sepals; petals 5, unequal, tomentellous on both sides, margins pectinate-fimbriate; disk fleshy, annular-pulvinate, conspicuously flattened at anthesis into a narrow, marginal flange, covering the bases of the petals; stamens 3, erect, but recurved after anthesis, with ribbon-like filaments, scarcely broadened at the base, anthers transversely ellipsoid, dehiscing by an extrorse, transverse, confluent cleft; ovary depressed and sharply trigonous, immersed in the disk, ovules 8-10 per locule, style fleshy, subulate, stigmas obscure. Fruits consisting of 3, free, divergent mericarps on a swollen receptacle, dehiscing along a median suture; seeds attached by a basal wing, embryoniferous part apical, wing much larger than the embryo.
Distribution
Africa present, Guianas present, Neotropics present, Pantropical present, Southern America: Bolivia (Bolivia present); Brazil North (Amazonas present, Pará present); Colombia (Colombia present); Panamá (Panamá present); Venezuela (Venezuela present), Terr. Roraima present, Trinidad present
Pantropical genus with 4 species in Africa, 2 in the Neotropics, occurring in Panama, Colombia, Venezuela, Trinidad, the Guianas, Brazil (Amazonas, Para, Terr. Roraima) and Bolivia.
Wood
Growth rings indistinct, if present, due to a narrow zone with less vessels.
Vessels diffuse, almost completely solitary, few radial pairs, 8-11 per sq. mm, round to oval, diameter clearly of two sizes, the narrow ones 50-80 μm wide, the wider ones 100-250 μm. Vessel-member length: 875(830-920) μm. Perforations simple. Intervascular pits rare, elongate, the slits often coalescent, 5 μm. Vessel-ray pits as the intervascular pits.
Rays uni- and multiseriate, 6-9 per mm of which 2-3 very wide, width 6-10 cells (= 100-160 μm). Heterogeneous, the uniseriates of square and upright cells, the multiseriates of rather low procumbent cells intermingled with square and intermediate-sized cells, up to over 750 cells (= 12 mm) high. Large bodies of silica abundant in the cells of the wide rays, occasionally some cells with rhombic crystals, also occasionally greenish yellow resin present.
Ground tissue of fibre-tracheids and septate fibres. Fibre-tracheids lumen 14-16 μm, walls c. 4 μm, with numerous small bordered pits on both radial and tangential walls. Septate fibres less numerous, scattered between the fibre-tracheids, lumen c. 16 μm, walls 2 μm. Length of fibre-tracheids: 1550(1480-1620) μm. F/V ratio: 1.66-1.83.
Vessels diffuse, almost completely solitary, few radial pairs, 8-11 per sq. mm, round to oval, diameter clearly of two sizes, the narrow ones 50-80 μm wide, the wider ones 100-250 μm. Vessel-member length: 875(830-920) μm. Perforations simple. Intervascular pits rare, elongate, the slits often coalescent, 5 μm. Vessel-ray pits as the intervascular pits.
Rays uni- and multiseriate, 6-9 per mm of which 2-3 very wide, width 6-10 cells (= 100-160 μm). Heterogeneous, the uniseriates of square and upright cells, the multiseriates of rather low procumbent cells intermingled with square and intermediate-sized cells, up to over 750 cells (= 12 mm) high. Large bodies of silica abundant in the cells of the wide rays, occasionally some cells with rhombic crystals, also occasionally greenish yellow resin present.
Ground tissue of fibre-tracheids and septate fibres. Fibre-tracheids lumen 14-16 μm, walls c. 4 μm, with numerous small bordered pits on both radial and tangential walls. Septate fibres less numerous, scattered between the fibre-tracheids, lumen c. 16 μm, walls 2 μm. Length of fibre-tracheids: 1550(1480-1620) μm. F/V ratio: 1.66-1.83.