北海道におけるカナワラビ属3種の比較生活史 Inter-specific comparison of the life history of three Arachniodes ferns in Hokkaido

北海道に生育するカナワラビ属3種の生活史を,垂直分布,生育場所,成熟開始,成熟度,葉形および葉数に着目し,胞子体の発達過程を通じて定量比較を試みた。北海道の11の山について垂直分布を調べると,シノブカグマ A. mutica, ナライシダ A. miqueliana, リュウメンシダ A. standishii では,それぞれ 925.6, 718.9, 565.4 m の平均標高に分布している。最大中軸分枝数 (MNV) は,それぞれ,59, 66, 79-NV であった。MNV は平均標高の増加に伴い減少する。成熟開始は相対的 (RDA, 比較発達齢,100×NV/MNV) にみると,64.4, 59.1, 60.8% で示され,垂直分布との相関は明瞭ではなかった。明るい落葉広葉樹林下に生育するナライシダが,最も早い成熟開始と高い成熟度を示した。葉形の確立過程を羽片軸の分枝数を用いて定量化してみると,シノブカグマとリュウメンシダは,三角状楕円形までは同じ過程をたどり,シノブカグマはさらに楕円状卵形に近づく。シノブカグマは MNV が最も少ないにも関わらず,葉数も増加させる傾向があり,3種の中では胞子体構造を最も分化させた種と思われる。一方,ナライシダの葉は三角形から五角形への変化が見られ,他の2種とは異なった確立過程をたどり,あわせて葉数も1〜2枚にとどまる。このように胞子体の発達過程にもとづき形態の定量比較をしたところ,ナライシダが他の2種とは,類似性が少ないことが示され,従来の類縁関係の評価と一致することが示された。

An inter-specific comparison of the life history of three Arachniodes ferns in Hokkaido was conducted, including their altitudinal distributions, habitat preferences, fertility, changes in leaf-shape and leaflet number during the sporophyte development. The average altitudinal distribution for A. mutica, A. miqueliana and A. standishii were 925.6, 718.9 and 565.4 m, above sea level on 11 mountains in Hokkaido, respectively. The maximum number of venation (MNV, the maximum number of midrib branches on the leaf in a population) was 59-NV, 66-NV and 79-NV, respectively. The average and MNV on fertile leaves decreased with increasing altitude. Initiation of the fertility (IF) in the relative developmental age (RDA, 100 ×NV/MNV) was 64, 59 and 61% in A. mutica, A. miqueliana and A. standishii, respectively. A. miqueliana, which occurred mainly on south-facing slopes on the deciduous forest floor, showed the earliest IF in the RDA among the three Arachniodes species. The leaf formation of A. mutica and A. standishii was similar to one another until the juvenile sporophyte. Thereafter, the leaf-shape inn A. mutica was transformed into the elliptical-oval shape. In addition, there was a slight increase in leaflet number during the compact developmental age expressed by NV. On the other hand, the leaf-shape of A. miqueliana changed from triangulate to pentagonal. These quantitative morphological comparisons made in the course of the sporophyte development seem to be valuable for the recognition of taxa, and furthermore to establish a sound classificatory system of a group in study.