Composite flower
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The
sunflower family or Family
Asteraceae (formerly
Compositae, also known as the
aster family) is a taxon of
dicotyledonous flowering plants.
The family name comes from the Genus
Aster and refers to the
star-shaped flower head of its members, typified as well by the
daisy. Asteraceae is the largest family in the Magnoliophyta with some 1,100 genera and over 20,000 recognized species. The common characteristic of all these plants—what in common parlance might be called a "flower"—is an
inflorescence or
flower head: a densely packed cluster of many small, individual
flowers, usually called
florets (meaning "small flowers").
Plants in the Family Asteraceae typically have one or both of two kinds of
florets. The outer perimeter of a flower head like that of a
sunflower is composed of florets possessing a long strap-like
petal, termed a
ligule; these are the
ray florets. The inner portion of the flower head (or
disc) is composed of small flowers with tubular
corollas; these are the
disc florets. The composition of asteraceous inflorescences varies from all ray flowers (like
dandelions, genus
Taraxacum) to all disc flowers (like
pineapple weeds).
The composite nature of the inflorescences of these plants led early taxonomists to call this family the Compositae. However, the rules governing naming conventions for plant families state that the name should come from the
type genus, in this case
Aster—thus Asteraceae. Indeed, this type of flower is no longer even called a "composite flower" as indicated above.
The numerous genera are divided into about 13 tribes. Only one of these,
Lactuceae, is considered distinct enough to be a subfamily (Subfamily
Cichorioideae); the remainer, which are mostly overlapping, are put in the Subfamily
Asteroideae (Wagner, Herbst, and Sohmer, 1990).
Many members of Asteracae are copious nectar producers, and are useful for evaluating
pollinator populations during their bloom.
Centaurea (knapweed),
Helianthus annuus (domestic sunflower), and some species of
Solidago (goldenrod) are major "
honey plants" for
beekeepers.
Solidago produces relatively high protein
pollen, which helps
honeybees overwinter.
Guayule—a source of
hypoallergenic latex—is in the Asteraceae.
References
-
- Walters, Dirk R. and David J. Keil (1996). Vascular plant taxonomy. 4th ed. Kendall/Hunt Publishing Company. Dubuque, Iowa.
- Wagner,W.L., D.R. Herbst, and S.H. Sohmer. 1990. Manual of the Flowering Plants of Hawai‘i, Vol. I. University of Hawaii Press, Honolulu. 988 pp.
