The families of gymnosperms
Vegetative. Small trees (rarely), or shrubs (mostly being shrubby switch plants, often rhizomatous), or vines (a few). Casuarina-like switch-plants photosynthesizing mainly via their grooved and jointed stems, the leaves reduced to small scales which are soon shed. Main branches whorled, or opposite. The leafy branchlets grooved-cylindrical, not flattened. Mature leaves simple (tiny, reduced); scale-like (unilacunar, with two leaf traces); opposite and decussate, or whorled (then usually in whorls of three).
Reproductive organization. Nearly always dioecious (but with occasional reports of bisexual inflorescences). The reproductive structures organized like reduced angiosperm flowers (with stamen-like antherophores, but with exposed, gymnospermous ovules). The ovules borne in female cones (the cones solitary or clustered at the compound inflorescence nodes, each consisting of a short-shoot bearing 2–4 pairs or whorls of overlapping bracts, the proximal bracts empty and the 1–3 terminal ones subtending female flowers). The seed-cone scales opposite and decussate, or whorled; commonly red, often fleshy. The ovules borne erect in the centre of the flowers; orthotropus (with an elongated, tubular micropyle); 1 integumented, or 2 integumented (depending on interpretation of the outer one, which may be interpreted as perianth).
Male inflorescences solitary or clustered at nodes, each composed of 2–8 descussate pairs or 3-part whorls of membranous bracts, the proximal ones empty; the male flowers with a perianth comprising 2 antero-posteriorly united, orbicular or obovate members, beyond which the prolonged axis bears 2–8 sessile or stipitate, 2-locular anthers. Pollen without air bladders. Pollination involving a liquid drop mechanism; anemophily is said to be prevalent, but with entomophily recorded in a few species.
Seeds and seedlings. Seeds one to three per cone, with no fleshy investment; wingless. Cotyledons 2.
Wood anatomy. Growth rings distinct (ring-porous). Secondary xylem with vessels. Normal vertical resin ducts absent.
Geography, cytology. Temperate to tropical; semiarid and arid areas in North America, Mexico, South America, Europe, Asia, and N and E Africa (including Canary Islands).
Taxonomy. About 40 species; Ephedra. Order Gnetales.
Comments. Several species yield ephedrine, an adrenalin-breakdown inhibitor widely used to relieve symptoms of asthma, sinusitis, etc.
Miscellaneous. • Ephedra: technical details (Le Maout and Decaisne).
To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2008 onwards. The families of gymnosperms. Version: 9th April 2015. delta-intkey.com’.