Taxodium L.C. Richard.
A genus of 3 species (as treated here), trees, of e. North America and Mexico. There has been much debate over whether the taxa of Taxodium should be treated as species or varieties, and if as varieties, the proper nomenclature. I agree with Godfrey (1988), in his preference "to recognize two species [within his area, which did not include the distribution of Taxodium mucronatum]... because it is my perception that the vast majority of trees (populations) are thus distinguishable." True intermediates appear to be very rare, though the "mimicry" of the two species creates "pseudo-intermediates" that can cause difficulties in identification. Occasionally, the Taxodium ascendens and Taxodium distichum can be seen growing together, in "hybrid habitats," as at the junction of Lake Waccamaw and the Waccamaw River (Columbus County, NC); a few recognizable intermediates can be seen. See Lickey & Walker (2002) for a contrary argument supporting varietal status. Neufeld (1986) discusses the different architecture and ecophysiology of the two species. The third taxon in the genus is Taxodium mucronatum Tenore, ranging from s. TX south to Mexico and Guatemala. West of the Mississippi River, the architecture of Taxodium distichum comes to resemble that of Taxodium mucronatum, suggesting the possibility of introgression. For this and other reasons, Watson in FNA (1993b) and other authors prefer to treat Taxodium mucronatum at varietal rank, as Taxodium distichum var. mexicanum Gordon. Taxodium is most closely related to Glyptostrobus and Cryptomeria.
Ref: Duncan & Duncan (1988); Godfrey (1988); Lickey & Walker (2002); Neufeld (1986); Page In Kramer & Green (1990); Tiwari et al. (2012); Tsumura et al. (1999); Watson (1993) In Flora of North America Editorial Committee (1993b). Show full citations.