Contributor
Nicola Biggs
Address
Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, UK
Description
Shrubs or small treelets 2-5m, branches pale grey-brown, often with thin, finely fissured bark, not lenticellate. Glabrous or hairy, the hairs normal and glandular. Stipules absent. Leaves evergreen, 4-50 x 2-26mm, whorled or (sub)opposite, simple; petiolate 0.5-2 mm long; petiole short pubescent; blades coriaceous, glossy above, matt and paler below, ovate, elliptic to oblong, the apex mostly emarginate at the apex, but sometimes obtuse, entire, with a slightly revolute margin, scabrous above, pubescent to nearly glabrous below, with some minute glandular hairs on both sides, midrib sunken above, prominent below. Inflorescence axillary, racemose; 1-7 flowered; peduncles and pedicels short, sparsely pubescent. Plants dioecious, some plants have functionally female flowers, in which anthers are present but no viable pollen is produced; the pollen grains are collapsed; other plants have functionally male flowers with a non functional ovary lacking style and stigma; their pollen viable. Flowers slightly zygomorphic (corolla only); calyx small, fused at base, lobes 5(6), base connate, sub equal, narrowly triangular, apex acuminate, sparsely pubescent or glabrous outside, ciliate, glabrous inside; corolla tube blue violet to purple, 5-9 mm long, broadly funnel-shaped with 5 lines of hairs outside below the lobes or glabrous, glabrous inside, lobes 5(6), imbricate in bud, sub equal, spreading, (sub)orbicular, sparsely pubescent outside, glabrous inside, ciliate; stamens 5(6), inserted on lower part of corolla tube, equal, slightly exserted, filaments 2-5 mm long, glabrous; anthers oblong, 1-1.2 x 0.6-0.8 mm, basifix, apex rounded, base deeply cordate, dehiscent by a longitudinal lateral split; style short, glabrous, stigma slender, twice dichotomously divided, minutely pubescent with glandular hairs above, slightly exerted; ovary superior, narrowly ovoid or oblong, nectariferous tissue at base, carpels (2)4, locule 1. Fruit a 2-valved capsule, 4-9.5 cm long, linear fusiform, glabrous, longitudinally ribbed. Seeds 1-4, 12-23 mm long, narrow, smooth, the apices with a pappus of unbranched hairs.
Distribution in Neotropics
Mexico, Guatemala, Nicaragua
Number of genera
Plocosperma buxifolium Benth. in W.J.Hooker, Icon. 12: 82, t.1195. 1876; Baillon, 1.c.; Solereder, 1.c. p.50; Blake, 1.c.
(P.microphyllum Baill. ex Solered. in Engl. & Prantl Nat. Pflanzenfam. 4, Ab. 2:50 (1895)) (P.anomalum S.F. Blake. Contr. U.S. Natl. Herb. 24: 17 (1922))
Status
Native, cultivated.
Key differences from similar families
Previously placed in Loganiaceae and left there by Leeuwenberg owing to the shape of the stigma and anthers and because of the absence of latex cells, even though it was the only member of the Loganiaceae to have a tuft of hairs on the seed. Leeuwenberg proposed that Plocosperma should be a monospecific genus of Loganiaceae.
The insertion of the hairs on the seed of Plocosperma is like that of Apocynaceae genera (Echites & Macrosiphonia) but it does not have the apocarpous fruit and partially sterile anthers. (Leeuwenberg)
The fruit of Plocosperma determines the placement of the genus. It is an elongated capsule, subterete, multicostate, 1-locular, 2-valvate, 1-4 seeded; the seeds are linear fusiform, with an ochraceous pappus like a brush of unbranched hairs at the apex. These characters exclude Plocosperma from Solanceae, Verbenaceae and Hydrophyllaceae.
Distinguishing characters (always present)
The elongated fruit is 1-locular and 2-valvate, with 1 to 4 linear seeds with an ochraceous pappus at the apex.
General notes
Three species were described but they cannot be clearly separated. The variation within the genus was based on differences in indumentum and the size of leaves, flowers and fruit. Guatemalan specimens have large leaves and Mexican specimens small leaves. The size of flowers and fruits is more or less correlated with leaf size. Leeuwenberg therefore recognizes P. microphyllum and P. anomalum as synonyms.
Important literature
Leeuwenberg, A.J.M. 1967. Notes on the American Loganiaceae 1 - Revision of Plocosperma Benth. Acta Bot. Neerl. 16(2): 56-61
Struwe, L. 2004. Plocospermataceae, Flowering Plants of the Neotropics.
Chiang & Frame 1987. The identity of Lithophytum. Brittonia 39(2)