Asteraceae Martinov. Aster Family.

Key to Asteraceae

A family of about 1500-1700 genera and 25,000-35,000 species, herbs, shrubs, trees, and lianas, cosmopolitan in distribution.

ID notes: Definitions primarily drawn from Roque et al. (2009). Discoid refers to heads consisting of only disk florets that are bisexual; disciform heads differ from discoid heads in that they have male or bisexual disk florets surrounded by naked florets or tubular female florets. Radiant heads are a type of discoid head, but the outer disk florets are larger, dilated, and often bilateral. This differs from radiate heads which have central disk florets of a similar size and outer ray florets. The flattened portion of a ray floret corolla is called a lamina. Liguliflorus heads consist of ligulate florets, which are perfect and bear a proximal tube and a distal, flattened, strap-like, 5-lobed bilateral corolla. The pappus is a modified (and usually reduced) calyx that can consist of bristles, scales, or awns (or sometimes a combination of these types). Pappus characters can vary substantially, and the nature of the bristles (plumose vs. barbellate or barbellulate) or scales (aristate, coroniform, etc…) are essential for composite identification. The pappus of bristles or scales aids in seed dispersal and often originates at the base of the cypselae (modified Asteraceae achene). The pappus is either persistent on the cypselae or falling, and will fall as one collective unit or individually. The calyculus is essentially the outer involucre or the outer "whorl" of involucre bracts subtending the true involucral bracts (phyllaries). Phyllaries are the collective bracts comprising the involucre of a composite head, and some involucres thus have a "lower" or "outer" whorl of bracts called the calyculus. The palea are bracts that sit at the base of individual disk or ray florets and are often referred to as "chaff", thus if a receptacle (basal part of head where palea are inserted) is naked it lacks chaff. If a head is epaleate it lacks palea.

Other Comments: {add to Key C: [Guizotia (abyssinica)]; [Heliomeris (multiflora var. multiflora)]; [Madia (sativa)]; [Tithonia ([diversifolia], rotundifolia)]}

Ref: Barkley, Brouillet, & Strother (2006) In Flora of North America Editorial Committee (2006a); Cronquist (1980); Roque et al. (2009). Show full citations.

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