Rubiaceae de Jussieu 1789
The Rubiaceae is a family of about 650 genera including some 13,000 species of herbs and shrubby plants and the fourth largest family of flowering plants after the Asteraceae, Orchidaceae and Fabaceae.
Important members of the family include Coffea (coffee), Gardenia, Cinchona (Quinine and other alkaloids), Rubia tinctorum (source of Madder, a natural dye) and bedstraws.
Succulent genera: Several succulent caudiciform genera, Anthorhizza, Hydnophtum, Myrmecodia, Myrmephytum, Phylohydrax and Squamellaria have commensal relationships with ants which nest in cavities in tubers or stems.
Hydnophytum Jack 1823 (Ant Plants)
(Greek: hydnon = truffle, tuber + phyton = plant)
Hydnophytum is an interesting genus of choice epiphytic caudiciform plants, with 55 species widely distributed on islands around the Indian and Pacific oceans including the Anadaman islands, Fiji islands, South-East Asia and Queensland Australia.
In their habitat, holes in the caudex are colonised by ants that protect their adopted plant against pests and provide some nutrients from faeces and other waste. Special nutrient-absorbing glands are produced within specialised warty regions of the chambers. The ants preferentially leave their waste in these warty parts. This symbiotic relationship allows the plants to obtain more nutrients than could be provided by the limited root system.
Some growers report that their local species of ants also make a home in these plants, although ants are not essential for these plants to grow. However, nutrients must be supplied in the form of fertiliser.
Hydnophytum species are best grown as epiphytes with the caudex completely exposed, on a bed of bark chippings (orchid compost) or secured to bark with some moss or osmunda fibre around the brittle roots to retain moisture. (Right)
These plants need continuous warmth with bright light. If conditions are not correct the caudex rapidly turns into a mush. As epiphytes, they need to be watered frequently, but allowed to dry out between waterings. When mounted on bark, watering should be more frequent. These plants can be propagated from cuttings of the branching stems, but it is not clear whether they will develop a proper caudex.