Genecological Studies on Plantago asiatica L. s. l.: Morphological Characteristics of a Dwarf Type of P. asiatica in the Shinto Shrine and Temple Ecosystem

Abstract

オオバコの種内変異を調査するため, 京都市北東部の8集団から得た系統を供試し, 同一条件下での栽培実験を行なった。さらに, 生育地の環境を調査して, 種内変異と生態分布との関連を検討した。1) オオバコの形態には著しい遺伝的変異が認められ, 普通型とminima型の2型が識別された。普通型では, 葉は大きく斜立し, 葉脈数は5で, 花序は長く, 斜立～直立し, 1蓋果は3～7個の大きな種子を結ぶ。minima型では, 葉は小さく傾伏し, 葉脈数は3で, 花序は短く, 傾上し, 1蓋果は4～10個の小さな種子を結ぶ。2) 普通型は, 畦畔や農道, 路傍, 未舗装の駐車場, 社寺林の林床などに生育していた。minima 型は神社や仏閣の境内に限って生育していた。3) minima型の生育地である神社の境内は, 薄暗く, 土壌中の窒素とリンの含量が普通型の生育地より低く, 維管束植物の多様度指数が低く, また毎日掃き掃除が行われるなど, 普通型の生育地とは環境条件や管理様式が顕著に異なっていた。そのため, minima型はストレスや撹乱の質と程度に関して普通型とは異なった環境に生育していると考えられた。オオバコの種内2型はこのような生育地の環境条件の違いに適応し, 住み分けているものと推定された。 A cultivation experiment was conducted on Plantago asiatica L. s. l. collected from eight natural populations in Kyoto City in order to detect intraspecific variation. Among the populations, there was a remarkable genetic variation in the morphological traits of the plants, and two intraspecific types, common and minima types, were distinguished (Fig. 2) as follows: common type: leaves larger, plagiotropic; veins 5; inflorescence longer, plagiotropic or erect; seeds larger, 3-7 per capsule; minima type: leaves smaller, decumbent; veins 3; inflorescence shorter, ascendent; seeds smaller, 4-10 per capsule. Based on the results of ANOVA for the quantitative traits of the plants, it was considered that some environmental factors of their habitats were closely related to the genetic variation of these two types (Table 2). Ecological distribution of these two types was investigated at 168 locations in Japan, and some environmental factors of the habitats were also defined for 11 populations in Kyoto City to examine their contribution to the ecological distribution. The common type was found on levees, paths between fields, roads, parking lots, shrine forest floors and so on, while the minima type was found only on the grounds of Shinto shrines and temples. The habitat of the minima type was characterized by relatively nutrient-poor soil, poor light conditions, low species diversity index and daily sweeping of the ground, which was remarkably different from those of the common type (Table 3), resulting in differences in the kind and intensity of stress and disturbance. The two intraspecific types of P. asiafica seem to have undergone a process of microevolution and maintained their habitat segregation as an adaptation mechanism to such different environmental conditions of their habitats.