Asteraceae Martinov. Common name: Aster Family.

Contributed by Alan S. Weakley and Scott G. Ward

Key to Asteraceae

A family of about 1800-1900 genera and 32,000-35,000 species, herbs, shrubs, trees, and lianas, cosmopolitan in distribution.

Key advice:Learning to recognize and key the genera of asters has a learning curve dependent on understanding specific morphology and terminology pertinent to the family; once understood, the seemingly belwildering diversity of the family becomes clearer. The definitions below are primarily drawn from Roque et al. (2009). Discoid refers to heads consisting of only disc 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 disc florets of a similar size and very obviously different 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 (e.g. Chichorium). 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 lower "whorl" of involucre bracts subtending the true involucral bracts (phyllaries). Phyllaries are the collective bracts comprising the involucre of a composite head. The pales are bracts (plural paleae) that sit at the base of individual disk or ray florets and are often referred to as "chaff"; if a receptacle (basal part of head where paleae are inserted) is naked or epaleate, it lacks chaff.

References: Barkley, Brouillet, & Strother (2006) In Flora of North America Editorial Committee (2006a); Correll & Johnston (1970); Cronquist (1980); Diggs, Lipscomb, & O'Kennon (1999); Powell & Worthington (2018); Roque, Keil, & Susanna (2009). Show full citations.

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