Studies on the Gymnocarpium robertianum complex in North America

The cytology and distribution of Gymrtocarpium robertianum (Hoffm.) Newman and G. jessoense (Koidz.) Koidz. subsp. parvulum Sarvela in North America are presented, together with the distinguishing features of these two species. Gymnocarpium robertianum is confirmed as a tetraploid species with 77=80 and the newly recognized G. jessoense subsp. parvulum also has n=80. In a previous paper (Sarvela, 1978) the senior author pointed out that of the six species of the genus Gymnocarpium in the world, two have a wide circumboreal range, G. dryopteris (L.) Newman and G. jessoense (Koidz.) Koidz., while the third species G. robertianum (Hoffm.) Newman, has a smaller distribution area. The genus Gymnocarpium in North America was last treated by Wagner (1966). He considered there were two basic species over most of the circumboreal range to which he applied the names G. dryopteris and G. robertianum. In addition, he introduced "the apparent cross of G. dryopteris and G. robertianum" as a new species of hybrid origin with the name G. heterosporum W.H. Wagner. G. dryopteris subsp. dryopteris has been known as a tetraploid since the work of Manton (1950) and eastern Canadian material was examined by Britton in 1953 (n = ca. 80). The larger, tripinnate taxon of the Pacific Northwest, G. dryopteris subsp. disjunctum (Rupr.) Sarvela, is a diploid (n — 40) (Wagner 1966). This has been sufficient reason for some workers to recognize the diploid entity as a separate species—G. disjunctum (Rupr.) Ching— although the relationship between the diploid and the tetraploid is obscure. New investigations (Sarvela, 1980) have indicated that the Gymnocarpium robertianum complex may include as many as four taxa, i.e. two species, G. robertianum and G. jessoense, and two hybrids, G. heterosporum W.H. Wagner (G. dryopteris X roberti anum) and G. X intermedium Sarvela (G. dryopteris X jessoense). Our studies indicate that G. X intermedium is a common hybrid of wide occurrence. So much so that, when this taxon is identified by its aborted spores and reduced glandularity, many sheets and localities of G. jessoense subsp. parvulum Sarvela are eliminated from consideration. The other hybrid, G. heterosporum, is con sidered to be rare indeed.