Annual or perennial herbs or small
subshrubs. Stems often 4-angled. Leaves opposite or in false whorls.
Stipular sheath present, divided into 1-many fimbriae. Flowers
bisexual, usually in axillary many flowered clusters (which may run
together to form a spike-like inflorescence); less often in terminal
capitula. Flowers frequently intermixed with numerous ±
scarious, filiform bracteoles. Calyx lobes 2-4(-8). Corolla
funnel-shaped or salver-shaped; lobes (3-)4. Stamens 4, anthers
usually exserted. Ovary 2-locular. Fruit usually a
2-valved capsule. Worldwide: c. 150 - 250 species, mainly America, but also widespread in the tropics and subtropics Burundi: 10 taxa. |
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