Amberboa spp.
Family: Asteraceae
Project: Southwest Biodiversity Consortium
Annuals or biennials, 20-70 cm; herbage not prickly, glabrate. Stems erect. usually branched from near bases. Leaves basal and cauline (distal smaller); petiolate (basal and proximal cauline) or sessile (distal cauline); blade margins dentate or ± lobed (basal) or entire to lobed (cauline). Heads ± radiant, borne singly. ( Peduncles slender. ) Involucres ovoid, 12-16 mm diam. Phyllaries many in several series, bases appressed, margins scarious, apices obtuse, inner with oblong, scarious appendages, these entire or spiny. Receptacles flat, epaleate, bearing setiform scales ('flattened bristles'). Florets many; corollas white to pink, purple, or yellow; outer sterile, corollas expanded, raylike, bilateral, 5-many-lobed; inner fertile, corollas actinomorphic; anther bases tailed, apical appendages oblong; styles branches: fused portions with basal nodes minutely hairy, distinct portions minute . Cypselae oblong, compressed, (apices denticulate), faces ribbed, wrinkled, with long, ascending hairs, basal attachment scars lateral, surrounded by whitish, swollen rims); pappi persistent, of many scales in several series, distinct, narrow [rarely 0]. x = 16. Amberboa has often been included within Centaurea, from which it differs by cypselae each with a denticulate apex and a conspicuous rim around the basal scar. The chromosome base number x = 16 is higher than that in most species of Centaurea in a strict sense. Molecular phylogenetic studies of the relationships of Cynareae genera (A. Susanna et al. 1995) place Amberboa as sister to the remaining genera of the Centaureinae.

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