| Popis: |
Two perennial species of wild geranium (Geranium nervosum Rydb. and G. richardsonii Fisch, and Trautv, [Geraniaceae]) which grow throughout the mountainous regions of western North America were studied to determine the factors influencing the life stage development and distribution of these plants. Attempts were also made to provide some information to assist in the taxonomy of this genus. Geranium richardsonii is found in wet meadows and along streambanks throughout its distribution. Geranium nervosum frequents rocky hillsides and drier meadows throughout its range. Seeds of G. nervosum had 65%, germination in the stratification pretreatment. Geranium richardsonii seeds required scarification to reach 60% germination. Both species germinated in excess of 80% when scarified and stratified. Overwinter survival experiments indicated that G. richardsonii could survive only in a wet meadow environment while G. nervosum could survive and establish in all three environments examined, wet meadow, dry hillside, and aspen (Populus tremuloides) grove. Both G. richarasonii and G. nervosum appeared to be limited by the same environmental factors although the degree of response was different. The seedling stage was the most responsive to environmental stress. Both G. richardsonii and G. nervosum seedlings had an optimum temperature range for survival of 20-25°C although they could and did adapt to lower temperatures. Seedlings of neither species could survive soil water potentials (Ψs) of -10 bars or lower. The adult stage of both species was more tolerant of s stress and G. nervosum adults could survive (Ψs) of -25 to -30 bars. Geranium richardsonii was less tolerant and appeared to limited by both Ψs and temperature in its distribution at the Forestry Field Station. The critical factors influencing the distribution G. nervosum and G. richardsonii were similiar but the species reacted to them in different ways. Geranium richardsonii was able to survive in environments that were highly saturated with water and under heavy cover. Geranium nervosum, although limited by temperatures above 32°C, was able to live in drier conditions by virtue of a tap root system. Hence, although the distribution of these two species was similiar, they were seperated by their response to environmental conditions. Hybridization is possible between G. nervosum and G. richardsonii, but the seedlings of these crosses were dwarfed and grew slowly. Crosses between these two species probably do not occur naturally. Geranium nervosum and G. viscossissimum crosses can occur naturally. Pollinators did not appear to distinguish between species, and seeds which were the result of hand pollination germinated and grew in the laboratory. It is not known whether the hybrids are fertile. Geranium nervosum and G. viscossissimum were also difficult to distinguish by morphological characteristics where the two species grew together. This indicates that some hybridization may have occurred. Geranium nervosum and G. viscossissimum also appear to have similar environmental requirements. This evidence indicates that G. nervosum and G. viscossissimum are probably not separate species. |
