A survey of seed and seedling characters in 1744 Australian dicotyledon species: cross-species trait correlations and correlated trait-shifts within evolutionary lineages

Seedling traits have been described across 1744 species of Australian plant s; Six traits were coded as binary alternatives: (1) phanerocotyly vs crypt ocotyly; (2) first leaf scale-like vs leaflike; (3) first leaf single vs pa ired; (4) cotyledons hairy vs, glabrous; (5) hypocotyl hairy vs glabrous, a nd (6) embryo green vs non-green at maturity. Seed volume was calculated fr om measurements of seed dimensions. Three approaches were used in analysing the data: (1) the taxonomic distribution of binary character states was de scribed; (2) the strength of bivariate character associations was quantifie d at species level ('cross-species' correlations and regressions); (3) the data were arrayed on a phylogenetic tree in order to analyse by 'phylogenet ic regression' for correlated evolutionary shifts in trait pairs. AU the tr aits appeared evolutionarily malleable. For example, while cryptocotyly was the minority condition (22% of species), it occurred in many different Lax a (124 genera, 40 families, 24 orders) with high levels of polymorphy (16%, 25% and 42% for genera, families and orders). Similarly, the less common a ttribute states for first leaf type, hypocotyl texture, cotyledon texture a nd embryo colour occurred in species From right across the dicotyledon phyl ogeny, as did independent evolutionary divergences in each of these charact ers. These patterns indicate that debate over which conditions are primitiv e and which are advanced will not have any general answer, only an answer f or a specific branch-step in the phylogenetic tree. In nearly all cases, co rrelated-divergence analyses showed the same patterns as cross-species anal yses. The strongest associations were between seed volume and cryptocotyly, seed volume and scale-like first leaf, and seed volume and presence of gre en embryo. In addition, cryptocotyly and scale-like first leaf, and cotyled on and hypocotyl type, were strongly associated in both correlated-divergen ce and cross-species analyses. Interpretation of results was mostly present ed with respect to seed size, a trait which we consider to be pivotal in a species' seedling establishment strategy. AU possible pairwise combinations of binary seedling traits were found in our study species. Taken together, the various lines of evidence presented here suggest that the traits have assorted more or less independently of each other and provide no evidence o f functional groups based on these attributes. Thus, the several existing s eedling typologies should be regarded as classifications of convenience rat her than as reflecting fundamental types. (C) 2000 The Linnean Society of L ondon.