The ginkgophytes are represented by a single extant species.  However, like the cycads, they have a fossil history that extends back to the Paleozoic and a flowering of abundance during the Mesozoic.  Also, the extant species is dioecious.  Vegetatively, however, the ginkgophytes more closely resemble conifers with woody monopodial growth, spur shoots and long shoots, and conifer-like roots.  The fan-like leaves of Ginkgo have a fern-like dichotomously branched veination.  Leaves of the long shoots have a notch in the middle of the fan to produce a bilobed leaf (this the name Ginkgo biloba).  The ovules and staminate strobili emerge from the spur shoots.  The ovules are borne in pairs at the tips of specialized and highly reduced megasporophylls.

The Tree of Life Project illustrates the ginkgophytes as a surviving seed fern.  Tudge (2000) shows them as a sister group to both the cycads and the conifers.  The molecular  evidence of Chaw et al. (1999) suggests a similar relationship. Even Pearson (1995) supports this view.  Descriptions of the groups and the taxonomic system follow Bold et al. (1987) and Bierhorst (1971).

I. PHYLUM CHARACTERISTICS

A. Structure

Habit: The ginkgos are conifer-like seed plants with fan-shaped leaves. The single extant species is dioecious.

Pollen: Pollen walls with 1 suture and no saccus. The microgametophyte has 2 prothallial cells, a stalk cell, 2 multiflagellate sperms and a tube cell.

Microstrobilus: Simple strobilus, open and pendant on spur shoots.

Seeds: Ovules with 3 integument tissue layers around a massive nucellus. Archaegonia (each with 2 neck canal cells) develop at the micropylar end of the megagametophyte. The embryo is dicotyledonous.

Megastrobilus: Simple, with 2 ovules on a long peduncle. This can be interpreted as an open compound strobilus if the whole spur shoot is viewed as a megastrobilus.

Stems: Monopodial growth with extensive wood. Leafy shoots of 2 types: long shoots and spur shoots. Reproductive structures occur only on the spur shoots. Stems with many mucilage canals.

Leaves: Fan-like with dichotomous branching of the veins. Leaves on the long shoots are notched while those on the spur shoots are not notched.

Roots: Like many of the conifers.

B. Ecology: The extant species occurs naturally in China but is widely planted throughout the temperate regions. These plants have a fossil history which dates from the late Paleozoic to the present. They were very abundant during the Mesozoic.

Taxonomy: As I have defined the phylum, the GINKGOPHYTA has a single class, GINKGOOPSIDA, with a single order, GINKGOALES.

example: Ginkgo.

revised: 04/15/2003