The families of gymnosperms
Vegetative. Pachycaul (fern-like rosette plants, with short, tuberous, irregularly branched subterranean stems producing relatively little wood, the leaf bases not persistent); evergreen; with apogeotropic roots bearing cyanobacteria, born in coralloid masses just above ground level. Not resinous (secreting mucilage). Mature leaves pinnate (the rachides with sub-circinate or conspicuously circinate vernation). The leaflets with pinnate venation, having a prominent midrib and dichotomously branching laterals. Mature leaves alternate.
Reproductive organization. Dioecious (via an XY chromosome system). The ovules borne in female cones; marginal or in notches, on discrete megasporophylls with sterile tips (the megasporophylls peltate). The megasporophylls 2 ovuled (the ovules on the inner-facing margins of the expanded hexagonal ends of the megasporophyll). The ovules orthotropus.
Pollen-sacs numerous, borne abaxially on peltate microsporophylls. Pollen without air bladders. Pollination probably anemophilous; involving a liquid drop mechanism. Fertilization involving spirally flagellate, motile spermatozoids.
Seeds and seedlings. Seeds large, with a fleshy investment; the fleshy investment developed from the integument (from the outer layer of the testa, which surrounds the woody inner one); wingless. Cotyledons 2.
Wood anatomy. Growth rings indistict (absent). Tracheids with opposite and multiseriate bordered pits (in Bowenia?), or with neither alternate nor opposite bordered pits (i.e., scalariform in Stangeria).
Geography, cytology. Temperate to tropical; South Africa (Stangeria), tropical Australia (Bowenia).
Basic chomosome number, n = 8 (Stangeria).
Taxonomy. 3 species; Stangeria and Bowenia. Order Cycadales.
Miscellaneous. • Bowenia serratula and Stangeria paradoxa: habit. • Stangeria paradoxa: male cone.
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’.