L., Sp. Pl. 570 (1753).
Derivation: Latin name of the plant; said to be derived from Hebrew mar, bitter; rob, much.
Synonymy: Not Applicable
Common name: None
Perennial shrubs with quadrangular branches becoming terete and woody at the base, villous to woolly with stellately branched hairs; leaves petiolate, opposite, dentate.
Inflorescence a loosely arranged thyrse with sessile cymose part-inflorescences usually with many flowers forming dense clusters around the nodes and with elongated internodes between them, with' bracts leaf-like and longer than the part-inflorescences; sepals more or less equally connate, with the 10 pointed lobes becoming stiff setae with a recurved apex, covered with stellately branched hairs; corolla 2-lipped, with a posterior lip narrowly oblong, stiffly erect, deeply 2-lobed, with an anterior lip with 2 narrow lateral lobes and the broadly spathulate central one; stamens 4 fertile, inserted at about the middle of the corolla tube; anthers with 2 cells fertile, diverging to about 90º from the attachment of the filaments, included; ovary deeply 4-lobed, with each locule with one basal ovule, with a gynobasic style and an included 2-fid stigma.
Fruit usually with 4 mericarps each oblong-obovoid with a distinct keel inside and along the margins, with the attachment scar small, ovate and at the base of the inside keel.
About 40 species from temperate Eurasia and the Mediterranean; 1 species naturalised in Australia.
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