Ginkgoaceae

Paleocene fossil

The Ginkgoaceae —a family of Ginkgoales— are arboreal gymnosperms with a single living representative today, of the genus Ginkgo and species Ginkgo biloba.

Description

Unlike cycads, and like almost all other gymnosperms, they are highly branched woody trees. It can be recognized by the fact that it has short branches in addition to long branches. Up to 30 m tall, with a more or less asymmetrical crown and gray, furrowed bark. Without resin channels. Leaves simple, spirally arranged, and widely spaced on long branches near branch tips, also widely packed on short branches on older trees, fan-shaped, bilobed or entire, deciduous and bright yellow in autumn, dichotomous venation. Dioecious trees, such as cycads. The pollen strobili of the male foot grow on sting-like stalks, consisting of a long central axis with lateral branches each bearing two microsporangia and pendulous, sometimes called "cones" but without sporophyll-like structures. The microsporangia dehiscence longitudinally, releasing the pollen grains. Non-winged pollen, and mobile sperm, ancestral character. Female feet do not wear "cones." The ovules occur in 2, terminal on a long branch from the stems like stingers, the seeds frequently 1 per branch (the other ovule immature to seed), about 2.5 cm in diameter, with a juicy external covering (sarcotesta) with an unpleasant odor, and another internal hard (sclerotesta). Inside the latter is the light green endosperm that constitutes the edible part of the "fruit". It is surrounded by a thin, more or less translucent, orange-brown envelope; the embryo is situated in an apical position. There are 2 or 3 cotyledons.

Ginkgo is one of the few plants with sex chromosomes. Plants with ovules carry two X chromosomes, while staminate individuals carry XY chromosomes.

Ecology

Sheets Ginkgo biloba

Currently limited to the remote montane valleys of China, it is endangered in the wild. Now, ironically, Ginkgo makes a good shade tree in urban situations, and has been planted all over the world as a popular sidewalk tree.

Little is known about the ecology of this species.

Pollination occurs by wind in the spring, but fertilization is delayed by 4-7 months. The juice and odor of the seed suggest animal dispersal, but the taxa that disperse it are unknown and may now be extinct.

Taxonomy and evolution

The group has been highly diversified in the past, but today there is only one genus (Ginkgo) with one species (Ginkgo biloba).

Classification considering extinct species

• Order Ginkgoales
  • Incertae sedis: †Sphenobaiera
  • † FamilyKarkeniaceae
  • † FamilyUmaltolepidiaceae
  • † FamilyYimaiaceae
  • † FamilySchmeissneriaceae
  • Family Ginkgoaceae
    • GenderBaieroxylon († speciesBaieroxylon cicatricum †Baieroxylon chilense †Baieroxylon implexum †Baieroxylon rockblanquense †Baieroxylon schuessleri)
    • GenderCheirophyllum ( species Cheirophyllum speculare)
    • GenderChiropteris ( † speciesChiropteris digitata †Chiropteris copypensis †Chiropteris zeilleri †Chiropteris barrealensis †Chiropteris reniformis †Chiropteris harrisii)
    • Gender Ginkgo († speciesGinkgo adiantoides †Ginkgo nicknames †Ginkgo beckii, Ginkgo biloba †Ginkgo bonesii †Ginkgo chloronoviae †Ginkgo crani †Ginkgo digitata †Ginkgo diminutive †Ginkgo dissect †Ginkgo gardneri †Ginkgo ginkgoidea †Ginkgo gomolitzkyana †Ginkgo huolinhensis †Ginkgo huttonii †Ginkgo jiayinensis †Ginkgo longifolius †Ginkgo manchurica †Ginkgo Occidentalis †Ginkgo oishii †Ginkgo pilifera †Ginkgo samylinae †Ginkgo sertensis †Ginkgo shiguaiensis †Ginkgo spitsbergensis †Ginkgo taipigensis †Ginkgo tatjanae †Ginkgo transsenonicus †Ginkgo tzagajanica †Ginkgo yimaensis †Ginkgo wyomingensis)
    • GenderGinkgoites ( † speciesGinkgoites huttoni †Ginkgoites acosmia †Ginkgoites antartica †Ginkgoites australis †Ginkgoites myrioneurus †Ginkgoites patagonica †Ginkgoites pluripartite †Ginkgoites obrutschewii †Ginkgoites tigrensis)
    • GenderGinkgoïdium ( † speciesGinkgoïdium bifidum †Ginkgoïdium nathorsti)
    • GenderGinkgomyeloxylon ( † speciesGinkgomyeloxylon tanzanii)
    • GenderGinkgopitys ( † speciesGinkgopitys chinense)
    • GenderPhoenicpsis
    • GenderPolyspermophyllum ( † speciesPolyspermophylum sergii)
    • GenderTrichopitys ( † speciesTrichopitys heteromorpha)

Classification according to Christenhusz et al.. (2011) for the living species

The classification, according to Christenhusz et al. 2011, which also provides a linear sequence of gymnosperms through genus:

• SUBCLASE II. Ginkgoidae Engl. in H.G.A. Engler & K.A.E. Prantl, Nat. Planzenfam. Nacht.: 341, 1897. Type: Ginkgoaceae.
  • Order B. Ginkgoales Gorozh, Lekts. Morf. Sist. Archegon.: 73, 1904. Type: Ginkgoaceae.
    • Family. Ginkgoaceae Engl. in H.G.A. Engler & K.A.E. Prantl, Nat. Pflanzenfam. Nachtr.: 19, 1897, Nom. cons. Type: Ginkgo L.

1 genus, 1 living species, China.

*3.1. Ginkgo L., Mant. 2: 313, 1771. Type: G. biloba L. Synonyms: Salisburia Sm, Trans. Linn. Soc. London 3: 330, 1797, nom. illeg. Type: S. adiantifolia Sm. (≡ Ginkgo biloba L.) Pterophyllus J.Nelson, Pinaceae: 163, 1866, nom. illeg., non Lév. (1844, Agaricaceae). Type: P. salisburiensis J.Nelson, nom. illeg. (≡ Ginkgo biloba L.)

Phylogeny

The broad, deciduous leaves of Ginkgo are not like those of most other gymnosperms. Sperm motility, known in other spermatophytes only in cycads, is clearly a primitive character, as is the lack of pollen tubes. The closest living group of Ginkgoaceae is that of the cycads (see Clade cycads + Ginkgo).

Evolution

The family has an extensive fossil record, but today contains a single living species. The first representatives of Ginkgo appear in the late Triassic, more than 200 million years ago, and the reproductive structures have changed little in their general appearance in about 120 million years. During the early Jurassic, the extinct relatives of Ginkgo were widely distributed and diverse, perhaps consisting of 3 families.

Economic importance

It has been planted around the world as a popular city sidewalk tree.