Monographs Details: Thlaspi montanum L. var. montanum x T. montanum var. siskiyouense P.K.Holmgren
Authority: Holmgren, Patricia K. 1971. A biosystematic study of North America Thlaspi montanum and its allies. Mem. New York Bot. Gard. 21: 1-106.

Crosses (Fig. 48) between these two varieties were successful 17-100% of the time with var montanum used as the seed parent and 0-100% of the time with var siskiyouense as the seed parent. In general, pollen stainability was high, ranging from 7-100% in the former crosses and 67-92% in the latter.

F1 hybrids were vegetatively vigorous, and, as in var idahoense, the only noticeable intermediate expression was in the basal leaves (Fig. 49). Herbarium specimens from the edge of the range of var siskiyouense indicate the intermediate nature of the basal leaves where var montanum has been in breeding contact with var siskiyouense.