Pollen morphology and trichome types of Betula spp. in the Hyrcanian forests of northern Iran

Pollen and trichome morphology of the genus Betula were evaluated from three main habitats in Iran using light and electron microscopy.Pollen types were identical and tri-porate;however,in terms of quantitative data,some differences were observed in exine(outside)wall thickness,length of polar axis and length of equatorial axis,possibly due to the environment.Pollen alone is insufficient to separate species of Iranian birch.Investigation of the trichome trait(small hairs or other outgrowths)revealed that birch species in Iran belong to:(1)Betula litwinowii Doluch.according to the low density of trichomes on the adaxial surface of the leaves and the lack of trichomes on the abaxial surface and many trichomes on the petioles;(2)Betula pendula Roth.due to the absence of trichomes on the adaxial surface and the low density of trichomes on the abaxial surface;and,(3)in the adaxial and abaxial surfaces of leaves and petioles,the trichomes had different types of pilose(long,soft hairs),and this strengthens the possibility of a different species or more likely a hybrid of B.pendula.