Gnetophytes

Phylum Gnetophyta

The Gnetophytes are an eclectic group of gymnosperms that appear to be closely related to angiosperms, although some phylogenetic evidence may indicate that the similarities are convergent evolution. There are three living genera: Gnetum, Ephedra, and Welwitschia. Of these, Ephedra, also known as Mormon's tea, is best known by the public as the source of ephedrine or pseudoephedrine. To botanists, Welwitschia is considered one of the strangest and sought-after plants growing only in the Namibian Desert of Africa. It only produces two leaves in its entire lifespan, and possesses a basal meristem which allows those leaves to grow for thousands of years.

Above: (left) Ephedra growing in an American desert; (center) Gnetum vine growing int he tropics; (right) Welwitschia growing in the Namibian desert

Ecology and Form

  • Gnetophytes are angiosperm-like gymnosperms with leaves, cones, and seeds that appear more like a flowering plant

  • Recent evidence that these angiosperm-like features are probably an example of convergent evolution

  • Gnetophytes may be a sister group to the flowering plants (anthophyte hypothesis), but other research indicates that they are more closely related to conifers (gnetifer hypothesis)

Stems

  • Gnetophytes are vascular plants with woody growth.

  • They exhibit vessels in their wood (secondary xylem); a cell type that is only known to exist in angiosperms

  • See below for differences between taxa

Leaves

  • Complex venation patterns in leaves

  • See below for differences between taxa

Roots

  • Welwitschia: very long taproot

Reproductive Structures

  • Flower-like cones with sterile bracts

  • Angiosperm-like seed in Gnetum with a pulpy seed coat

  • Double fertilization, a feature supposedly unique to angiosperms, has been observed in both Gnetum and Ephedra (Friedman & Carmichael 1996)

Above: Vessel of Ephedra

Geologic Age

Classification

└Lignophytes

└Spermatophytes

└Gnetophyta

Diversity

Three orders: Ephedrales, Gnetales, and Welwitschiales

Gnetales

  • 1 genus: Gnetum; more than 30; less than 45 species

  • G. gnemon is called gnemon, melinjo, belinjo, kuliat/culiat, bago, bigo and padi oats or paddy oats

  • Stems: woody, tropical vine

  • Leaves: angiosperm-like; ovate with drip-tip

Above: Gnetum, showing the leaves and developing seeds

Left: Male cones of Gnetum

Ephedrales

  • 1 genus: Ephedra; over 70 species

  • Called joint-pine, joint-fir, Mormon-tea, Brigham tea, or mahuang

  • Stems: horsetail-like appearance with a woody trunk

  • Leaves: reduced, non-functional leaves

Above: Male cones on Ephedra, growing in the Inyo National Forest, in the White Mountains, eastern California.

Right: Close-up of a female cone of Ephedra

Above: Ephedra growing in the Rock Garden at NYBG

Welwitschiales

  • 1 species: Welwitschia mirabilis

  • Called welwitschia, tree tumbo, kharos, khurub, tweeblaarkanniedood, nyanka, or onyanga

    • In Afrikaans, “tweeblaarkanniedood” means “two leaves that cannot die.”

  • Stems: short and stump-like

  • Leaves: Only two leaves with a basal meristem that allows continuous growth

Above: young specimen of Welwitschia, showing the stem with an indeterminate meristem and the two leaves of the plant, which will split length-wise

Above: Male cones of Welwitschia

Below: Female cones of Welwitschia

Evolutionary relationships

The evolutionary relationships of gnetophytes to other seed plants remains elusive and several hypothesis have been proposed:

Anthophyte hypothesis

Gnetifer hypothesis

  • In this hypothesis, the gnetophytes are a sister group to the conifers, and the gymnosperms are a monophyletic group, sister to the angiosperms

Gnepine hypothesis

  • In this hypothesis, the gnetophytes belong within the conifers as a sister group to the Pinaceae, this the conifers are not monophyletic

Additional Resources