Isoëtes (Quillworts)

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Isoëtes

Isoëtes spp.
(Photograph from C. Taylor)

Isoëtes is a genus of "primitive" plants containing 200 or more species, found throughout the world. A typical Isoëtes plant consists of a buried rootstock bearing a rosette of simple, linear leaves (sporophylls). Each sporophyll contains four longitudinal, septate canals and an ovoid sporangium near its base. Each sporangium contains either scores of globose megaspores or thousands of ellipsoid microspores. A flap of tissue, called the velum, partly or completely covers the sporangium. Above the sporangium is a triangular ligule.

Below are shown two phylogenetic or evolutionary trees based on molecular data. Figure 1 shows a phylogenetic tree for species found throughout the world based on nuclear ITS and chloroplast rbcL-atpB spacer sequence data. Figure 2 is a phylogenetic tree for species found in the "North American" species complex based on ITS and LEAFY homolog sequence data.

This research was funded by the National Science Foundation

Figure 1. Worldwide phylogeny of Isoëtes based on molecular sequence data. Numbers above lines are number of substitutions supporting each node; those below line are bootstrap values. Tree is rooted with I. coromandelina. (Tree from Hoot and Taylor 2001).

Fig. 2. Phylogeny of North Amerian Isoëtes based on ITS and LEAFY homolog sequence data. Numbers above and below lines are as above. (Tree from Hoot and Taylor 2001).

Bibliography:

Hoot, S. B., W. C. Taylor, and N. S. Napier. 2006. Phylogeny and biogeography of Isoëtes based on nuclear and chloroplast DNA sequence data. Systematic Botany 31: 449-460.

Schuettpelz, E. and S. B. Hoot. 2006. Inferring the root of Isoëtes: Exploring the alternatives in the absence of an acceptable outgroup. Systematic Botany 31: 258-270.

Hoot, S. B., N. S. Napier, and W. C. Taylor. 2004. Revealing unknown or extinct lineages within Isoëtes (Isoëtaceae) using DNA sequences from hybrids. American Journal of Botany 91: 899-904.

Taylor, W. C., A. R. Lekschas, Q. F. Wang, X. Liu, N. S. Napier, and S. B. Hoot. 2004. Phylogenetic relationships in Isoëtes (Isoëtaceae) in China revealde by nucleotice sequences of the nucler ribosomal ITS region and the second intron of a LEAFY homolog. American Fern Journal 94: 196-205.

Hoot, S. B. and W. C. Taylor. 2001. The utility of nuclear ITS, a LEAFY homolog intron, and chloroplast atpB-rbcL spacer region data in phylogenetic analyses and species delimitation in Isoëtes. American Fern Journal 91: 166-177.