HOOT, SARA B.1*, W. CARL TAYLOR2, and NANCY S. NAPIER1. 1Department of Biological Sciences, University of Wisconsin, Milwaukee, WI 53201; 2Botany Department, Milwaukee Public Museum, Milwaukee, WI 53233. - Parental species of Isoetes allotetraploids, including “dead-beat” parents.
Nucleotide sequences from the highly variable second intron of a
LEAFY homolog (a meristem identity gene) were used to determine
the parents of allotetraploid Isoetes species. By comparing
the positions on the cladogram of the two cloned sequences from the
allotetraploids with an extensive sampling of sequences from diploid
species, parental species were identified. In some cases, we have been
able to identify both parents with some certainty. For example, the
allotetraploid I. maritima from the Pacific Northwest
resulted from a hybridization event between I. echinospora
(circumboreal) and I. bolanderi (Pacific Northwest and
Rockies). Isoetes tuckermanii (northeastern North American)
resulted from a cross between I. engelmannii (eastern North
America) and a species with sequence similarities to I. prototypus
(northeastern North America). In other cases, we have been able
to identify only one of the parents; the other "dead-beat"
parent is missing from our data set. For example, I. appalachiana
(southeastern U.S.) is a cross between I. engelmannii
and an unknown taxon with affinities to I. flaccida
(Florida). I. azorica (Azores Islands) resulted from a
hybridization event between I. engelmannii and a missing or
undiscovered Isoetes species from North America or the
Mediterranean region. A previous hypothesis had suggested that I.
azorica was morphologically similar to I. tuckermanii .
The fact that I. azorica and I. tuckermanii both
have I. engelmannii as one of their parents may account for
such an interpretation.
Key words: allotetraploids, hybrid origins, Isoetes, sequence data