Pollen morphology of tribes Aptosimeae and Myoporeae supports the phylogenetic pattern in early-branching Scrophulariaceae revealed by molecular studies

摘要

Pollen morphology of six species representing three genera of tribe Aptosimeae and six species representing two genera of tribe Myoporeae (Scrophulariaceae) is described and illustrated using light microscopy (LM) and scanning electron microscopy (SEM). Pollen grains in Aptosimeae are 3-syncolporate, prolate, sometimes oblate-spheroidal in shape; mainly medium-sized, occasionally in some taxa small; exine sculpture striate, rarely with microperforations and small granules. Pollen grains in Myoporeae are 3-colpate-diorate, spheroidal, rarely oblate-spheroidal or prolate in shape; mainly medium-sized, occasionally in some taxa small; exine sculpture foveolate, microreticulate, rugulate-microperforate, rugulate, sometimes with small granules. Two major pollen types, 3-syncolporate (Aptosimeae) and 3-colpate-diorate (Myoporeae) are recognized by aperture types. Within these pollen types, eight subtypes are distinguished (three in Aptosimeae, five in Myoporeae) based on pollen size, exine sculpture and details of colpi and endoapertures. Our analysis of palynomorphological data (both published earlier and newly reported here) outlines the same main clades as those revealed by molecular phylogenetic studies, corresponding to Aptosimeae, Leucophylleae+Myoporeae and Androya, which differ by their pollen aperture types: 3-syncolporate, 3-colpate-diorate, and 3-colporate, respectively. There are also some differences in exine sculpture patterns. Thus, palynomorphological data are mainly consistent with recent results of molecular phylogenetic studies. Considerations on ancestral pollen character states in early-branching Scrophulariaceae are provided. It is assumed that the colporate type was probably ancestral in Scrophulariaceae; however, the ancestral status of the colpate type cannot be excluded as well.