Close (microscopic) examination of the megaspores is often required to distinguish species in this family. However, based on the descriptions of the three species known to occur in Southeast Alaska (and excluding potential hybrids), it may be possible to recognize these to species in the field. In particular, Western Quillwort (Isoëtes occidentalis) is said to have rigid leaves and an unpigmented sporangium wall, whereas the other two have pliable leaves and usually brown streaked sporangium walls. Leaves of Spiny-spore Quillwort (Isoëtes echinospora) appear to be significantly larger than those of Maritime Quillwort (Isoëtes maritima), the latter only growing to 12 cm, while the former grow to 20cm (and larger).
|Scientific Name||Common Name||Summary|
|Isoëtes echinospora||Spiny-spore Quillwort||Expected to occur throughout the region (see FNA range map), but apparently few collections, including at least two on Baranof Island and one on Prince of Wales Island.|
|Isoëtes maritima||Maritime Quillwort||Expected on islands and the northern gulf coast. Apparently only a few collections including from Shelter Island, Prince of Wales Island, Revillagigedo Island, and the Yakutat Forelands.|
|Isoëtes occidentalis||Western Quillwort||Primary range seems to be well south of the region (FNA Map), though there are apparently a few scattered reports in south coastal Alaska. In Southeast Alaska this species has so far only been reported from Baranof Island.|
|Isoëtes x truncata||Quillwort Hybrid||Hybrids of Western Quillwort (Isoëtes occidentalis) with Maritime Quillwort (Isoëtes maritima) or Spiny-spore Quillwort (Isoëtes echinospora) have been given this name and may be found in the region.|