Bedstraw (Rubiaceae)

Description

The Rubiaceae are morphologically easily recognizable as a coherent group by a combination of characters: opposite leaves that are simple and entire, interpetiolar stipules, tubular sympetalous actinomorphic corollas and an inferior ovary.A wide variety of growth forms are present: shrubs are most common (e.g. Coffea, Psychotria), but members of the family can also be trees (e.g. Cinchona, Nauclea), lianas (e.g. Psychotria samoritourei), or herbs (e.g. Galium, Spermacoce). Some epiphytes are also present (e.g. Myrmecodia). The plants usually contain iridoids, various alkaloids, and raphide crystals are common. The leaves are simple, undivided, and entire; leaf blades are usually elliptical, with a cuneate base and an acute tip. In three genera (Pavetta, Psychotria, Sericanthe), bacterial leaf nodules can be observed as dark spots or lines on the leaves. The phyllotaxis is usually decussate, rarely whorled (e.g. Fadogia), or rarely alternate resulting from the suppression of one leaf at each node (e.g. Sabicea sthenula). Characteristic for the Rubiaceae is the presence of stipules that are mostly fused to an interpetiolar structure on either side of the stem between the opposite leaves. Their inside surface often bears glands called "colleters", which produce mucilaginous compounds protecting the young shoot. The "whorled" leaves of the herbaceous Rubieae tribe have classically been interpreted as true leaves plus interpetiolar leaf-like stipules. The inflorescence is a cyme, rarely of solitary flowers (e.g. Rothmannia), and is either terminal or axillary and paired at the nodes. The flowers are usually bisexual and usually epigynous. The perianth is usually biseriate, although the calyx is absent in some taxa (e.g. Theligonum). The calyx has four or five sepals with basally fused lobes. The corolla is sympetalous with four or five lobes, mostly actinomorphic, usually tubular, mostly white or creamy but also yellow (e.g. Gardenia spp., Mycelia basiflora), and rarely blue (e.g. Faramea calyptrata) or red (e.g. Alberta magna, Ixora coccinea). They have four or five stamens, which are alternipetalous and epipetalous. Anthers are longitudinal in dehiscence, but some genera are poricidal (e.g. Rustia).