Rotheca is a genus of flowering plants in the family Lamiaceae (order Lamiales), comprising an estimated 35 to 60 species of shrubs, subshrubs, and herbaceous perennial plants, with a few species growing as lianas or small trees. The great majority of species are native to Sub-Saharan Africa, while three species occur in tropical Asia. When any part of the plant is damaged, it emits a distinctly unpleasant odor — a characteristic shared with its close relatives.
The flowers are among the most recognizable features of the genus. The corolla is typically blue, purple, or white (rarely yellow) and divided into five lobes, with the lower (abaxial) lobe often enlarged and differently colored, giving many species a striking, asymmetrical appearance. Four long stamens extend well beyond the petals. The fruit resembles a drupe but eventually breaks apart into four single-seeded mericarps.
For most of the 20th century Rotheca was subsumed within the broader genus Clerodendrum. The genus was resurrected in 1998 following molecular phylogenetic analyses that demonstrated Clerodendrum, as then circumscribed, was polyphyletic. Rotheca can be distinguished from Clerodendrum by a suite of morphological characters, including its unlobed ovary at anthesis and its actinomorphic, non-accrescent calyx.
The type species, Rotheca serrata, is native to tropical Asia and has a history of medicinal use there. Rotheca myricoides, native to tropical East Africa, is widely cultivated as an ornamental throughout the tropics for its vivid blue flowers.
Etymology
The genus name Rotheca was coined by the American botanist Constantine Samuel Rafinesque in 1838 as a Latinization of a Malayalam word meaning "small teak." The original Malayalam name has been recorded with widely varying spellings over the centuries.
Distribution
Most species of Rotheca are native to Sub-Saharan Africa, with only three species occurring in tropical Asia. The ornamentally important Rotheca myricoides is native to tropical East Africa and has been widely introduced throughout the tropics as a garden plant.
Taxonomy Notes
Rotheca was first described by Rafinesque in 1838 but was absorbed into the broadly defined genus Clerodendrum by John Isaac Briquet in 1895, a treatment that prevailed for roughly a century. Doubts about the grouping persisted, and in 1998 molecular phylogenetic work demonstrated that retaining Rotheca within Clerodendrum renders the latter polyphyletic, prompting the genus's revival. The type species is Rotheca serrata (the original name Rotheca ternifolia is now considered illegitimate). Transfer of Clerodendrum species into Rotheca continues incrementally, largely driven by compilation of regional floras.
