Rubioideae

Rubioideae is the largest subfamily within Rubiaceae, the plant family that also includes coffee. It encompasses a wide range of growth forms, from herbs to shrubs, and has a broad distribution across tropical, subtropical, and temperate regions worldwide. The subfamily contains thousands of species grouped into numerous genera, with Rubia, Galium, Asperula, and Houstonia among the better known examples.

A characteristic feature of Rubioideae is the presence of interpetiolar stipules, a common Rubiaceae trait that forms a ring around the stem at the leaf bases. Leaves are typically opposite. Flowers are usually small and actinomorphic, often arranged in inflorescences such as cymes or heads. Floral parts are commonly in multiples of four or five, and the corolla is often tubular or funnel-shaped. The fruit is frequently a capsule or berry, though fruit type can vary by genus.

Taxonomically, Rubioideae is divided into multiple tribes, reflecting its wide diversity. Representatives include Galieae (containing Galium and Asperula) and Rubieae (containing Rubia), among others. The exact tribal composition varies with different taxonomic treatments and ongoing phylogenetic studies.

Molecular studies support Rubioideae as a major clade within Rubiaceae, and ongoing research continues to clarify intertribal relationships and genera boundaries within the subfamily. The group includes several genera of horticultural and historical interest, such as the madder (Rubia) for dye and the common bedstraw (Galium).

The name Rubioideae derives from the genus Rubia, one of its representative and historically significant genera.