Southwest Desert Flora

The Rubiaceae family is large, the 4th largest flowering family, with more than 600 genera and almost 14,000 accepted species names. Members of this family include annuals and perennials including trees, shrubs, a few lianas and herbs; shrubs are the major forms. They are distributed throughout the world in almost every region with the largest diversities in the tropics and sub-tropics. In North America there are 90 genera with about 500 accepted taxa overall.

Common family characteristics: Leaves: simple, shape and form variable from one eco-region to the next, i.e. leaves are needle- or scale-like in desert areas, margins entire, leaves undivided, opposite, stipules present on the stem, leaves often whorled .

Inflorescence: typically a cyme, or seldom with solitary flowers. Flowers: often bisexual, calyx has either 4 or 5 sepals, usually fused (sympetalous); corolla also has 4 or 5 petals, often fused and actinomorphic, flowers mostly white and often tubular, few stamens 4 or 5. Fruit: fruit is variable with several types including berry, capsule, drupe or schizocarp, fruits often red.

The largest genus in the Rubiaceae family is Psychotria with about 1,800 species. In North America there are 40 species. Several genera, about 30, have more than 100 species and a little over 100 genera are monotypic.

Economic Importance: the most economically important species in Rubiaceae is the genus Coffea from which coffee is grown commercially. Coffee is one of the most important commodities in the world, second only to petroleum. Other plants of economic importance include the genus Cinchona, a tree whose bark is a source of the alkaloid Quinine which is produced and used to treat Malaria; Galium odoratum is a small plant that contains “coumarin” which is a natural precursor of warfarin, also known by the brand name Coumadin, an anticoagulant in use since 1954. Coumadin has been used as a pesticide since 1948 and is still in use for this purpose; Carapichea ipecacuanha is the source of the emetic ipecac. Rubiaceae also contains species (Rubia) that are used in the preparation of dyes (Rubia tinctorum, red dye) and other species used as ornamental cultivars (Bouvardia, (bluets), Cephalanthus, Gardenia, Houstonia, Isora, Pentas). There are no known significant food staples in this family.

Members of Rubiaceae from Arizona have minimal economic importance.

North America is not well represented with large numbers of species of the Rubiaceae family. Some species, such as Cephalanthus, are found over large geographic areas but have only a couple of genera and not very many species. Here are most of the larger genera and their approximate number of species in parenthesis; Galium (85), Spermacoce (19), Houstonia (18), Oldenlandia (9), Guettarda and Diodia with (8) species each. Cephalanthus is not a large North America genus but is found over a large geographic area.