 Huernia macrocarpa Hydnophytuman ant plant The Gentianales is an order of 6 families and around 5500 species of flowering plants including the Apocynaceae (periwinkle family), Gentianaceae (gentian family), Loganiaceae (strychnine family), Oleaceae (olive family), Rubiaceae (gardenia, coffee and quinine family).
Leaves of Gentianales are opposite and internal phloem is within the wood (except in Rubiaceae). Many species contain alkaloids, some of which are very toxic and others widely used in beverages e.g. Coffea (coffee) or as medicinal drugs Cinchona (quinine). The Gentian Family Gentianaceae is of horticultural importance to growers of alpine plants.
Most of the succulent species are found within the Apocynaceae, including the Subfamily Asclepiadaceae which includes many stem succulents and vining plants, generally with a milky sap containing latex and various alkaloids. The Apocynaceae also includes the horticulturally important succulent caudiciform genus Adenium (Desert Rose) and spiny succulent caudiciforms in the genus Pachypodium.
The Rubiaceae includes a number of interesting caudiciform succulents that provide homes for commensal ants within cavities in their caudexes. The ants provide a degree of protection for these plants.
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Families of Succulent Plants 
