A family with a single genus: Cycas
Habit: dioecious palm like shrubs with aerial or subterranean, pachycaul,
Leaves: pinnate, spirally arranged, produced in seasonal growth flushes
interspersed with cataphylls, lower leaflets often reduced to spines.
Longitudinal ptyxis erect or rarely reflexed, horizontal ptyxis circinate.
Leaflets with a single thick midrib and no lateral veins; stomata
confined to abaxial surface in most species; individual ptyxis involute.
Leaves pubescent, at least when young, with branched or simple transparent
Microsporophylls: aggregated into determinate male cones and each with
a simple sterile apex, which is often produced into an upturned spine.
Each microsporophyll bearing numerous microsporangia (pollen sacs) on
its abaxial surfaces. Microsporangia opening by slits. Pollen cymbiform,
Megasporophylls: loosely or tightly imbricate, spirally arranged in an
indeterminate terminal rosette with the central axis continuing vegetative
growth. Ovules two to many (rarely one), marginally inserted on the stipe
and directed obliquely outwards (`ascending'). Megasporophyll apically
dilated into a pinnatifid, pectinate, toothed or entire lamina in the
distal zone beyond the ovule-bearing stipe.
Seeds: subglobular to ellipsoidal, with a yellow, orange or brown fleshy
outer sarcotesta, and with or without spongy tissue beneath the inner
woody sclerotesta. Endosperm haploid, derived from the female gametophyte.
Embryo straight; with 2 cotyledons that are usually united at the tips
and a very long, spirally twisted suspensor. Seeds platyspermic;