Relationships in the Botrychium campestre (Ophioglossaceae) complex

Botrychium campestre and B. lineare have, since their original descriptions, been considered closely related due to their morphological similarity. Although B. lineare was initially thought to be very rare, subsequent discoveries of many additional populations, especially in the Rocky Mountains and Sierra ranges, have afforded the opportunity to analyze hundreds of specimens on the basis of allozyme genetics. Surprisingly, B. lineare demonstrates a high degree of heterozygosity, implying an outcrossing breeding system, unlike the mostly homozygous, selfing B. campestre. However, overall levels of Nei's Genetic Identity between the two taxa are higher than usual between species. With this knowledge, we infer that taxon lineare is probably ancestral within complex, and that taxon campestre arose from within it as an adaptation to more xeric habitats. Given that B. campestre has nomenclatural priority, we propose to recognize lineare as a variety within a more broadly construed campestre, i.e., Botrychium campestre var. lineare, and suggest that hybrid or introgressed plants, such as rarely occur (e.g., at Glacier National Park and in the Black Hills of South Dakota) be referred to only at the specific rank, i.e., without reference to variety.