Trichome anatomy and taxonomy of Saxifraga (Saxifragaceae)

Abstract

Trichomes on flower pedicels and leaves were examined in 213 species of Saxifraga L. and in the monotypic, segregate genera Zahlbrucknera Reichenb., Saxifragella Engl., Saxifragodes D. M. Moore and Saxifragopsis Small. Pedicel trichomes were found to be better taxonomic characters than foliar ones. Six main trichome types were identified: i) multiseriate, glandular; ii) uniseriate, glandular; iii) sessile, multicellular, glandular; iv) multiseriate, eglandular; v) uniseriate, eglandular; vi) unicellular, eglandular. The different types were distributed (except in certain species) on pedicels as follows. Multiseriate, glandular types occur in four series of Saxifraga sect. Micranthes (Haw.) D. Don, part of sect. Gymnopera D. Don, and in sects Ciliatae Haw., Trachyphyllum Gaudin, Xanthizoon Griseb., Ligulatae Haw., Porophyllum Gaudin, Porphyrion Tausch and Irregulares Haw. They also occur in the genus Saxifragopsis. Uniseriate, glandular types occur in five series of Saxifraga sect. Micranthes, part of sect. Gymnopera and Irregulares, and in sects. Miscopetalum (Haw.) Sternb., Cymbalaria, Griseb. Tridactylites (Haw.) Engl., Saxifraga and Stoloniferae Haw. They also occur in the genus Zahlbrucknera. Eglandular, multicellular trichomes occur occasionally in Saxifraga sects Micranthes and Gymnopera, more frequently in sects Ciliatae and Ligulatae, and are ubiquitous in sects Xanthizoon, Porophyllum and Porphyrion. Eglandular, unicellular trichomes occur only in Saxifragopsis and Saxifragodes. Sessile, glandular trichomes occur in a group of species from Saxifraga sect. Stoloniferae. Saxifragella is glabrous. This taxonomic distribution of trichome types generally supports Engler's classification of the genus, and is compatible with other evidence from palynology, embryology and seed morphology. The taxonomic disposition of the few exceptional species is discussed.