Comparative life history of five HokkaidoPolystichum ferns with reference to leaf development in relation to altitudinal distribution

Abstract

The temperate fernsPolystichum craspedosorum, P. retroso-paleaceum, P. tripteron, P. braunii andP. microchlamys are distributed widely in Hokkaido: on 13 Hokkaido mountains their average altitudinal distributions are 450, 479, 570, 689 and 964 m above sea level, respectively. The developmental stage of the sporophytic leaf is expressed by the “number of venation” (NV, the number of veins branching from the midrib of the leaf), which, inPolystichum ferns, is itself a qualitative expression of the phase-change from sterile to fertile leaf production and is more discriminatory than leaf area, length or dry weight. Usually, the developmental stage structure of the fertile leaf expressed by NV in the fivePolystichum ferns showed a normal distribution. Among the fourPolystichum ferns that grow in the forest understory of Hokkaido's cool temperate regions, a good correlation was found between the mean altitude of vertical distribution and the maximum NV of the leaf (r=−0.993) and the initiation of maturity in the relative developmental stage (r=0.991) of the ferns.Polystichum craspedosorum found on cliffs, however, matures at much earlier stage and has the smallest maximum NV. In the developmental stage expressed by the NV, the initiation of fertility and maximum NV seem to be correlated with altitudinal distribution and habitat in populations ofPolystichum ferns in Hokkaido.