Abstract
The Isoetes engelmannii complex of eastern North America consists of 30 taxa including 13 named species. Nine of the 17 hybrids within the complex (the largest group of Isoetes hybrids in the world) have been formally described. Those named hybrids are reviewed here in light of recent additions to and enhancements of the morphological and cytological evidence employed in their original description. The pedigree of three of these, I. ×brittonii, I. ×bruntonii and I. ×carltaylorii, is updated and clarified. Formal descriptions are proposed for two additional taxa: I. ×fernaldii, hyb. nov. (I. engelmannii × I. hyemalis) and I. ×karenae, hyb. nov. (I. appalachiana × engelmannii). The potential for a further eight hybrid combinations to occur in the wild is also addressed.
Highlights
Nine sterile hybrid combinations in the Isoetes engelmannii complex are reviewed in light of ecological, distributional and taxonomic information developed since their original description
Hundreds of I. appalachiana and scattered I. engelmannii plants were found in ephemeral swales and side channels along a permanent stream (Rowanty Creek) in seasonally flooded deciduous swamp forest (Figure 3)
Isoetes engelmannii is common 100-200 m upstream along the creek as well
Summary
At 17.6% (N=6, four plants as listed below), the average velum coverage of the sporangium of the hybrid is intermediate between putative parents I. engelmannii (10-15%) and I. appalachiana (20-25%) (Brunton and Britton 1997).
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