Aster (family Compositae) A genus of mostly perennial herbs in which the leaves are simple and spirally arranged, the flower heads have imbricate bracts and flat, naked receptacles; ray florets, usually present, are white, blue, or red, but never yellow but the disc florets are yellow. The achenes are flattened and smooth with a pappus of short, bristly hairs. Many N. American species are cultivated as Michaelmas daisies and have become naturalized in Europe and elsewhere. There are about 250 species, mostly northern temperate.

as·ter / ˈastər/ • n. 1. a plant (genus Aster) of the daisy family that has bright rayed flowers, typically purple or pink. Many species, including the New England aster (A. novae-angliae), bloom in autumn.2. Biol. a star-shaped structure formed during division of the nucleus of an animal cell.

aster A starlike arrangement of microtubules radiating from a centrosome. Asters become conspicuous in animal cells at the ends of the spindle when cell division starts. They are believed to help locate the spindle in relation to the cell's boundaries and to trigger cleavage of the cytoplasm when nuclear division is completed.

aster A group of microtubules that radiates out from each centriole pair during cell division in animal cells.

aster genus of plants with radiated flowers. XVIII. — modL. use of L. astēr — Gr. astḗr STAR.