The utility of the morphological variation of pollen for resolving the evolutionary history of Billia (subfam. Hippocastanoideae, Sapindaceae). Issue 3 (28th October 2014)

• Record Type: Journal Article
• Authors: Harris, AJ; Lutz, Sue; Acevedo, Pedro; Wen, Jun
• Is Part Of: Journal of systematics and evolution. Volume 53:Issue 3(2015:May)
• Page Start: 228
• Page End: 238
• Publication Date: 2014-10-28
• Subjects: Plants -- China -- Classification -- Periodicals; Plants -- Classification -- Periodicals; 580.12
• DOI: 10.1111/jse.12130
• Languages: English
• ISSNs: 1674-4918

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <sec id="jse12130-sec-0001" sec-type="section"> <p>In this study, we examined the utility of pollen morphology for resolving questions about the evolutionary history of <italic>Billia</italic>, which is a poorly known genus of Neotropical trees. <italic>Billia</italic> has been traditionally circumscribed with two species and treated as sister to <italic>Aesculus</italic> L. However, the number of species in <italic>Billia</italic> is uncertain, because the genus exhibits abundant morphological diversity but little discontinuous variation. Therefore, <italic>Billia</italic> may be monotypic and highly polymorphic, or it may have two species with blurred boundaries due to incipient speciation and/or hybridization. Moreover, one recent molecular phylogenetic study shows <italic>Billia</italic> nested within <italic>Aesculus</italic>. Our work sought to address the following questions: (i) Are there discontinuities in the pollen of <italic>Billia</italic> that may suggest species boundaries? (ii) Does the pollen of <italic>Billia</italic> show evidence for inter‐specific hybridization? (iii) Do the exine morphology and size of pollen in <italic>Billia</italic> differ from those in <italic>Aesculus</italic>? Our results from scanning electron microscopy showed that pollen exine morphology is not taxonomically informative in <italic>Billia</italic> but that there are significant differences in pollen size between red‐ and white‐flowered individuals. Thus, our pollen data support the utility of flower color in <italic>Billia</italic> for species delimitation. Our assessments of pollen viability do not support hybridization in the genus, but cannot be used to rule it out. Finally, pollen exine morphology may lend some support to an evolutionary origin of <italic>Billia</italic> within eastern North American <italic>Aesculus</italic>. In contrast, data on pollen size suggest that <italic>Billia</italic> may belong in a topological position outside of <italic>Aesculus</italic>.</p> </sec> </abstract>