Abstract/Summary

Aesculus L. is a small genus of horticulturally important trees and shrubs comprising 13 species. Frequent hybridization among species, particularly in cultivation, has contributed to taxonomic confusion and difficulties in identification of plants. At the same time, disease is threatening the future of some species in horticulture. One species, A. hippocastanum, is emerging as a model for documenting phenological responses to climate change, but it is unclear whether there is significant intraspecific variation in this species. These factors have prompted the morphological and molecular reconsideration ofAesculus taxonomy, with emphasis on plants in horticulture in the UK, and the investigation of the inter-and intra-specific variation in phenology for these species. A detailed morphological study based on 101 morphological characters scored 48 plants. Multivariate analyses and scrutiny of the data against the existing descriptions of species, varieties and cultivars, including hybrids, were used to identify plants, but highlighted the deficiencies of current identification tools .. The plants from the morphological study were included In a molecular survey. New sequence data for one nuclear (ITS) and two chloroplast regions (trnHK, matK) were generated. Bayesian phylogenetic analyses of these sequence data, along with published data, supported previously existing infra-generic lineages. However, no evidence for intraspecific lineages of A. hippocastanum was found in the morphological or molecular analyses. A phenological survey of plants on the University of Reading Whiteknights campus was made for 51 plants, 34 of A. hippocastanum and 17 representing other species. For two years, each plants' phenological stage (budburst, leaf development, shoot development, flowering, fruiting and beginning of dormancy) was recorded. Consistently early trees and early species were identified. For A. hippocastanum the number of days between the first tree's bud burst and the last tree's budburst was 29 days in 2013 and 38 days in 2014; the time between the earliest bud burst in 2013 and in 2014 was 13 days. Thus, intraspecific variation in budburst time within years is much greater than inter-annual differences.