"With few exceptions, nature uses the second arrangement of fibers for her internally pressurized, water-filled cylinders. These structures (often termed 'hydrostatic skeletons' or 'hydroskeletons' as well as 'hydrostats') have helical reinforcing fibers. And this particular arrangement is no rare or once-evolved thing. It occurs in the stems of young herbaceous (nonwoody) plants such as sunflowers; it provides a wrapping for flatworms (platyhelminths and nemerteans), roundworms (nematodes), and segmented worms (annelids); it stiffens the body wall of sea anemones; it determines the response to muscle contraction of the outer mantle of squids; and it's a major functional component of shark skin. The material of the fibers varies widely, the functions of these hydroskeletons are even more diverse, but the wrapping is almost always helical." (Vogel 2003: 409) Learn more about this functional adaptation.
Steven Vogel. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
Barcode of Life Data Systems (BOLD) Stats Specimen Records:18871 Specimens with Sequences:22269 Specimens with Barcodes:11021 Species:6954 Species With Barcodes:6668 Public Records:13513 Public Species:5972 Public BINs:0
The Asteraceae (Compositae, alternate name) with its approximately 1,620 genera and more than 23,600 species is the largest family of flowering plants (Stevens, 2001). The family is distributed worldwide except for Antarctica but is especially diverse in the tropical and subtropical regions of North America, the Andes, eastern Brazil, southern Africa, the Mediterranean region, central Asia, and southwestern China. The majority of Asteraceae species are herbaceous, yet an important component of the family is constituted by shrubs or even trees occurring primarily in the tropical regions of North and South America, Africa and Madagascar and on isolated islands in the Atlantic and Pacific Oceans. Many species of sunflowers are ruderal and especially abundant in disturbed areas, but a significant number of them, especially in mountainous tropical regions, are narrow endemics. Because of the relentless habitat transformation precipitated by human expansion in montane tropical regions, a number of these species are consequently in danger of extinction.
The family contains several species that are important sources of cooking oils, sweetening agents, and tea infusions. Members of several genera of the family are well-known for their horticultural value and popular in gardens across the world and include zinnias, marigolds, dahlias, and chrysanthemums. The commercial sunflower genus Helianthus has been used as a model in the study of hybridization and its role in speciation (Rieseberg et al., 2003). See list of economically important Asteraceae
Herbs, suffrutices, shrubs or (rarely) climbers or trees. Leaves alternate, less often opposite. Stipules 0, but false stipules occur in a few species (for example: Vernonia myriantha and Senecio deltoideus) . Flowers small (florets), aggregated into heads (capitula) and simulating single larger flowers and surrounded by a calyx-like involucre of one or more series of bracts (phyllaries). Receptacle of the head expanded, with or without receptacular scales or bristles each subtending a floret. Florets all similar sexually (head homogamous) or central and marginal florets differing (head heterogamous) and then the central florets usually bisexual or rarely male, the outer female or rarely neuter. Calyx never typically herbaceous but represented by a pappus of numerous simple or feathery (plumose) hairs, or a smaller number of membranous scales, teeth or bristles, or by a continuous membranous ring; sometimes 0.
Corolla composed of (3-)5 united petals fused into a tube below and with a distal limb consisting of either: (1) 5 actinomorphic lobes or teeth (tubular florets); or (2) a unilateral strap-shaped limb (ray) 0-3(-4)-dentate at the apex; or (3) a unilateral strap-shaped limb (ligule), 5-dentate at the apex.
Stamens 5, borne on the corolla-tube; anthers usually fused into a cylinder around the style. Ovary inferior, 1-celled, with 1 basal ovule; style single below but branching above into 2 stigmatic arms. Fruit an achene, crowned by the pappus, sometimes with a slender beak interposed between them.