Tuesday, August 7, 2012

Isoeteaceae Rchb.

Quillwort family

Among my favorite plants are the quillworts, or Isoetes. Though little known outside of botanist circles, the quillworts are a fascinating and unusual family of non-flowering plants.

Isoetes occidentalis L. F. Henderson thrives underwater
The family dates back to the early Carboniferous period, where they were the dominant plant type in many of the large swamp and woodland areas. After the late Devonian drying, the quillworts declined considerably. Today, they are comprised of a single genus, Isoetes, among which there are roughly 200 extant species.

In California, there are a total of 6 fully recognized species of Isoetes. Three of these are aquatic plants, and must be continually submerged under water. Two are found in vernal pool systems, and are able to survive desiccation during the hot summer months. One of the species is fully terrestrial, but is still found in mostly wet habitats.

Isoetes bolanderi Engelmann can survive out of water
The stem of an Isoetes plant is distinctive, in that it does not produce roots like euphylophytes (ferns, horsetails, conifers and flowering plants), but rather, uses modified leaves as its root structures. Also, the leaves themselves are interesting in that they are not homologous structures to the leaves of euphylophytes, but rather, were independently evolved (i.e. analogous structures).

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