Arran whitebeams complex fashion, which involved the common whitebeam ("Sorbus aria") giving rise to the tetraploid rock whitebeam ("Sorbus rupicola") which is still found on Holy Isle. This species is able to survive at higher altitudes and therefore occupies a less competitive niche with fewer tree species able to tolerate the harsher conditions. The rock whitebeam interbred with the rowan / mountain ash ("Sorbus aucuparia") to produce the hybrid, a fertile separate species the Scottish whitebeam ("Sorbus arranesis") which grows well in this zone of reduced competitive growth at higher altitudes. The bastard mountain ash ("Sorbus pseudofennica") arose from a further cross
Insecticidal soap at higher concentrations or at temperatures above 32 °C (90 °F). Plant injury may not be apparent until two days after application. Some plant species are particularly sensitive to soap sprays. Highly sensitive plants include: horse chestnut, Japanese maple ("Acer"), "Sorbus aucuparia" (mountain ash), Cherimoya fruit, "Lamprocapnos" (bleeding heart), and sweet pea. Other sensitive plants are, for example: "Portulaca", some tomato varieties, "Crataegus" (hawthorn), cherries, plum, "Adiantum" (maidenhair fern), "Euphorbia milii" (crown of thorns), "Lantana camara", "Tropaeolum" (nasturtium), "Gardenia jasminoides", "Lilium longiflorum" (Easter lily). Conifers under (drought) stress or with tender new growth are sensitive as well. Damage may occur