Equisetaceae
Equisetophyta (Arthrophyta). The Equisetaceae are terrestrial, herbaceous, homosporous
vascular plants comprising a single genus with about 15 species. The free-living
sporophytic plant body consists of a rhizome with adventitious roots, and an aerial
portion with ribbed, silicified stems that are hollow except at the jointed nodes which
bear whorls of reduced scalelike megaphyllous leaves, sometimes alternating with branches.
Clusters of 5-10 eusporagia hang from the margins of umbrellalike sporangiophores that are
aggregated into a compact strobilus at the tip of the shoot axis. In some species the
fertile shoots have little chlorophyll and may also be differentiated from the vegetative
shoots in other ways. The spores have 4 straps of tissue called elaters that uncoil from
the wall and extend in response to a decrease in humidity, thereby facilitating spore
dispersal. The free-living bisexual or male gametophytes are irregularly lobed, tiny
ribbonlike photosynthetic structures, often found on the surface of mud. Multiflagellated
sperm produced in an antheridium must travel through a film of water in order to reach the
egg of an archegonium and initiate the zygote that may develop into a new sporophyte
individual.
Each "thumbnail" image below is linked to a larger photograph.
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Equisetum x schaffneri (E. giganteum x E. myriophyllum), horsetail or
scouring rush. Note whorled branches. The stems are ribbed and are hollow except at the
jointed nodes. Cells in the stem may be silicified or glasslike, contributing to the
utility of the stems in scouring pots and pans, a quality that was exploited by pioneers
in western North America. |
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Equisetum hyemale, scouring rush. Whorls of leaves and the terminal strobilus
are clearly visible. The amber colored umbrellalike sporangiophores are evident and a few
pendulous pale yellowish sporangia are partially visible. |
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Equisetum arvense, horsetail. This species normally has the strobilus borne
on short, non-green, ephemeral shoots that appear early in the growing season. The green
shoots develop later, by which time the fertile shoots usually have wilted. In this
population, an aberrant green shoot with a developing strobilus was found long after the
normal non-green fertile shoots had senesced. |
Non-Flowering Plant Family Access Page
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