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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.

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.

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

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Hover over a shape, letter, icon, or arrow on the map for definition or see the legend. Data for arrows not developed for genera and families which may have species only occurring outside the flora area.

image of plant© Gary P. Fleming | Hieracium | Original Image ⭷
image of plant© Keith Bradley | Solidago | Original Image ⭷
image of plant© Alan Cressler: Ampelaster carolinianus, Juniper Creek, Juniper Prairie Wilderness, Ocala National Forest, Marion County, Florida 4 by Alan Cressler | Ampelaster carolinianus source | Original Image ⭷
image of plant© Will Stuart | Elephantopus | Original Image ⭷
image of plant© Keith Bradley | Achillea | Original Image ⭷
image of plant© Gary P. Fleming | Lactuca | Original Image ⭷
image of plant© Aidan Campos | Dracopis source | Original Image ⭷
image of plant© Bruce A. Sorrie | Eupatorium | Original Image ⭷
image of plant© Aidan Campos | Sonchus source | Original Image ⭷
image of plant© Gary P. Fleming | Euthamia | Original Image ⭷
image of plant© Scott Ward | Chrysopsis | Original Image ⭷
image of plant© Scott Ward | Helianthus | Original Image ⭷
image of plant© Gary P. Fleming | Artemisia | Original Image ⭷
image of plant© Alan Cressler: Helenium vernale, Apalachicola National Forest, Franklin County, Florida 1 by Alan Cressler | Helenium source | Original Image ⭷
image of plant© Alan M. Cressler | Silphium | Original Image ⭷
image of plant© Keith Bradley | Echinacea | Original Image ⭷
image of plant© Keith Bradley | Palafoxia | Original Image ⭷
image of plant© Gary P. Fleming | Doellingeria | Original Image ⭷
image of plant© Bruce A. Sorrie | Packera glabella | Original Image ⭷
image of plant© Alan M. Cressler | Pityopsis | Original Image ⭷
image of plant© Gary P. Fleming | Aster tataricus | Original Image ⭷
image of plant© Gary P. Fleming | Solidago squarrosa | Original Image ⭷
image of plant© Gary P. Fleming | Oclemena | Original Image ⭷
image of plant© Keith Bradley | Rudbeckia | Original Image ⭷
image of plant© Alan Weakley | Iva source | Original Image ⭷
image of plant© Gary P. Fleming | Pilosella | Original Image ⭷
image of plant© Keith Bradley | Facelis retusa | Original Image ⭷
image of plant© Alvin Diamond, some rights reserved (CC BY-NC), uploaded by Alvin Diamond | Tithonia rotundifolia source | Original Image ⭷
image of plant© Scott Ward, some rights reserved (CC BY), uploaded by Scott Ward | Verbesina occidentalis source | Original Image ⭷
image of plant© Richard & Teresa Ware | Marshallia mohrii | Original Image ⭷

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