Apocynaceae  

Recent molecular phylogenetic research suggests the inclusion of Asclepiadaceae and Periplocaceae in Apocynaceae (Endress & Bruyns 2000).

Species of Ceropegia L. are rather popular as ornamentals (indoors). The genus occurs as an escape in green houses in the  Botanic Garden in Meise.

1. Flowers solitary in the leaf-axils. Corolla usually blue (rarely pink or white in cultivation), showy (25-50 mm across). Seeds without a plumose appendage at apex. Plant creeping === Vinca

1. Flowers in axillary and/or terminal umbels or corymbs. Corolla pink (Asclepias) or greenish-white, rarely dark purple, less than 15 mm across. Seeds with a plumose appendage at apex. Plant erect or slightly twining, not creeping === 2

2. Inflorescence a few-flowered corymb. Follicle (fruit) smooth === Vincetoxicum     

2. Inflorescence a many-flowered umbel. Follicle spiny === 3

3. Rootstock fibrous, never tuberous. Flowers white, in extra-axillary umbels. Follicle inflated === Gomphocarpus

3. Rootstock napiform-tuberous. Flowers pink to purplish, in terminal umbels. Follicle not inflated === Asclepias

Additional alien: Periploca graeca L. (SE-Eur., SW-As., garden escape) (see Lambinon 1995).  

Literature

Endress M.E. & Bruyns P.V. (2000) A revised classification of the Apocynaceae. Botanical Review 66: 1-56.

Lambinon J. (1995) Notes taxonomiques, nomenclaturales et chorologiques relatives à la quatrième édition de la « Nouvelle Flore » de la Belgique et des régions voisines. 3. Données nouvelles sur des plantes adventices ou subspontanées en Belgique. Dumortiera 60: 1-36.