APOCYNACEAE Juss.
Family composed of about 375 genera and about 4500-5500 species of trees (few), shrubs, lianas or herbaceous plants, widely distributed through tropical, subtropical and temperate regions of the world. Currently it includes genera belonging to the “old” families Periplocaceae (Subfam. Periplocoidae) and Asclepiadaceae (Subfam. Asclepiadoidae). In North African the family, broadly defined, is represented by 19 genera and 28 species.
Although many species are tall trees typical of tropical rainforests, they are especially abundant in tropical dry environments (xeric). There are also perennial herbs from temperate zones. Many of these plants have a milky latex, and many species are poisonous if ingested. Many genera such as Adenium or Carissa, produce both sap and a milky latex, and others, such as Pachypodium, have clear sap and no latex.
Key to genera
1 Plant not cactiform, with woody stems 2
1 Plant cactiform, with succulent stems 11
2 Plant spiny. Fruit in berry Carissa
2 Plant unarmed. Fruit in follicle 3
3 Follicles arranged in pairs, opposite to each other on base which is semifused Periploca
3 Follicles arranged differently 4
4 Tree (rarely large sized shrub) with large oval-oblong leaves (8-15 cm wide) Calotropis
4 Shrubs or subshrubs with small leaves (less than 5 cm wide) 5
5 Shrub with retamoid appearance, leafless stems, young branches with leaves, but small (0.5-1.5 × 0.2-0.35 cm) and promptly deciduous Leptadenia pp
5 Shrub not retamoid, well developed leaves, larger, persistent 6
6 Anthers free. Style 1. Follicle with brown hairs Nerium
6 Anthers adnate (fused together congenitally) Styles 2. Follicle without brown hairs 7
7 Follicles with bristles or spines 8
7 Follicles smooth 9
8 Leaves cordate Pergularia
8 Leaves not cordate Gomphocarpus
9 Woody climber Leptadenia pp
9 Shrub not climbing 10
10 Plant tomentose (except fruits) Vincetoxicum
10 Plant glabrous Solenostemma
11 Stems erect, thin, from subcylindrical to tetrangular, gradually tapering at the apices; inflorescences, with 1-4 flowers, forming false racemes along the elongated apical portion of the stem 12
11 Climbing stems, from ascending to erect, tetrangular; with blunt or slightly but abruptly tapered apices; inflorescences in axillary pseudo-umbels or in solitary subaxillary flowers 13
12 Leaf rudiments 4-12 mm long, accompanied at the base by stipular glands Caudanthera
12 Leaf rudiments 1-5 mm long, accompanied at the base by tufts of stipular hairs Caralluma
13 Inflorescences with 1-9 flowers, not arranged in terminal pseudo-umbels Apteranthes
13 Inflorescences of 20-30 flowers (if less, then the stems have evaginations almost conical and pointed) arranged in terminal pseudo-umbels 14
14 Stems whose ribs appear evaginations almost conical and pointed, which are arranged in two opposite segments Orbea
14 Stems without evaginations almost conical and pointed Desmidorchis
Updated by: J.F. Mota & F.J. Pérez García.