Petal epidermal micromorphology in holoparasitic Orobanchaceae and its significance for systematics and pollination ecology

Abstract

Flowers of holoparasitic plants have evolved several adaptations for pollination as part of their parasitic strategies. A study of the petal epidermis may be useful to systematics as well as to the knowledge of ecological and co-evolutionary adaptations between the parasites and their pollinators. The present work is a comparative study of the microsculpture of nectar guides and landing platforms in the flowers of holoparasitic species in the family Orobanchaceae. In total, 285 samples of 39 species from 10 holoparasitic genera (Boschniakia C.A.Mey. ex Bong., Boulardia F.W.Schultz, Cistanche Hoffmanns. & Link, Conopholis Wallr., Diphelypaea Nicolson, Epifagus Nutt., Mannagettaea H.Sm., Orobanche L., Phacellanthus Siebold & Zucc. and Phelipanche Pomel) and as an outgroup, of six additional hemiparasitic genera (Castilleja Mutis ex L.f., Euphrasia L., Orthantha (Benth.) A.Kern., Parentucellia Viv., Rhinanthus L., and Striga Lour.) were analysed using both light and scanning electron microscopy. Types of epidermal cells were characterised, and their distribution on the adaxial and abaxial surfaces of the petals determined. The following four major epidermal types were recognised: tabular rugose striate cells (TRS), areolate cells (AS), papillose conical cells (PCS) and lobular striate cells (PLS). Two main types of trichomes were observed, namely glandular and non-glandular. Our results showed that petal micromorphology may be useful to systematics; its influence in relation to the pollinators is discussed.