SPECIES OF THE WEEK

 

Maria Graham

Rachelle Acosta

Biology 100L

Mr. Richard Jensen M.S.

March 31, 1997

 

 

Scientific name: Equisetum laevigatum

Common name:            Horsetails or scouring rush

Kingdom:                     Plantae

Division:                       sphenophyta

Class:                           sphenopsida

Order:                          equisetales

Family:                         equisetaceae

Genus:                          Equisetum

Species:                        laevigatum

 

 

Equisetales, among all other orders of the class Sphenopsida, is the only one that lives today.  The others: Hyeniales, Pseudobornials, Sphenophyllales and Calamites are only known because of the fossils they left behind.  The majority of information gathered for this group of herbaceous, vascular plants is due primarily to the study of the Equisetum genus.  Equisetum plants are generally found in damp or moist places below 8,000 feet.  Many are found in Southern California, but others are all over the country and even the world.  In Britain, one might find E. telemateica -- the tallest of them all, E. sylvaticum, E. palustre, E. arvense and E. pratense.  In the U.S. the tallest of the horsetails was the 40 ft E. giganteum until the 60 foot relative was located in Britain.  Equisetum can be traced back to the Coniferous geological epochs. 

Equsietum have underground rootstocks, jointed stems and whorled branches and leaves shooting out from the nodes.  The leaves can be scale-like and there are formations of sporangia on the peltate sporophyll.  The branches get bushy kind of like an actual horse's tail, hence the common nickname "horsetails''.  On the surface are glasslike deposits of silicon dioxode, also known as silica, which is why some people have used this plant for scouring pots and pans.  Higher up in the taxonomic classification, it's division, Sphenophyta, means "wedge plants" which is very similar to the related Sphenophyllum which means "wedge leaf".  Unfortunately, the Sphenophyta group is now extinct. 

The genus Equisetum contains twenty-five different species, including E. laevigatum, the species of the week.  They have aerial stems that last a year or two, usually without branches, but with long sheaths dilated upward.  It's obtuse cones are brown to yellow in color and contain spores.  This is the species that would be found here in the Southern Cailfornian area.  "The gametophyte of the Equisetum plants...show that the primitive pteridophytic gametophyte was thallose, more or less elongate, and more than one cell in thickness," (Willis, 1966). The sex organ usually is usually located on the dorsal side of Equisetum plants. 

Horsetails are  commonly compared to ferns but they're leaves are distinctly originated from flattened branches and have become small and scale like.  Ferns have the green leaves, horsetails do not.  Though Fern and Horsetails have evolved differently from each other, the many similarities point to a common branching somewhere along the way is in many cases we find in biology. 

Our perennial herb sends shoots up yearly: one is a green shoot with a reproductive spike at the end, the other reproductive shoot does not contain chlorophyll and arrives earlier in the year.  Interestingly enough, the horsetails also undergo hibernation as well as vegetative reproduction. 

Some species of Equisetum, as mentioned previously, are found in Britain.  The wood horsetails are found in the woods, have delicateand barren stems with long down-curving branches.  The marsh Horsetails, found on swamp ground, are barren as well but have branches and are fertile.  The field Horsetails are very widespread and have rhizomes embedded in soil which makes them a pest that is very difficult to get rid of.  The blunt-topped Horsetail also found in Britain have fertile stems that are barren and they appear simultaneously.  Our species of the week, E. laevigatum is found in communities here in U.S. is usually unbranched but very long and bushy, just like the horse's tail.

 

Sources:  Benson, et. al. Plant Classification, 2nd Ed. Lexington, Massachusettes. D.C. Heath         and Company. 1979.

  Boedjin, et. al. Plants of the World. New York, New York. E.P. Dutton & Company,     Inc. 1968.

  Munoz, et. al. A Flora of Southern California. Berkeley and Los Angeles, California.     University of California Press. 1974.

  Scagel, et. al. Plants: An Evolutionary Approach. Belmont, California. Wadsworth           Publising Company, Inc. 1955.

  Smith, et. al.Cryptogamic Botany, Vol. II, 2nd Ed. McGrawhill Book Company, Inc.     1955.

  Willis, et. al. A Dictionary of Flowering Plants and Ferns, 7th Ed. New York, New         York.Cambridge University Press. 1966.