Ginkgo biloba is dioecious, a character in common between Ginkgo and the living cycads. Pollen is produced in paired microsporangia (also termed sporangiophores) on simple stalked microsporophylls, which are spirally aggregated into simple catkin-like strobili (lacking bracts), which are also carried on short shoots. The pollen grains are monosul-cate, spherical and wind-dispersed (see also Foster and Gifford, 1989).
Ovules are erect and borne in pairs subtended by a collar of uncertain origin on axillary stalks on short shoots. The ovule has a single integument that becomes three-layered and develops in the seed into a fleshy outer sarcotesta, a stony inner sclerotesta and a thin endotesta. This is superficially similar to integument differentiation in the cycads and Medullosa, and is an adaptation to animal dispersal.
Development of the male gametophyte is very similar to that in the cycads except that there are two prothallial cells instead of one. The mature spermatozoid is similar to the cycad sperm, but it is smaller and has only 2.5 turns of the spiral, compared with 5 or 6 in the cycads. Numerous flagella (10,000-12,000 in cycads, uncounted in Ginkgo) are attached along the spiral.
Was this article helpful?