Evolution, phylogeny, and systematics of the Juglandaceae

A comprehensive systematic investigation was conducted on the extant Juglan daceae based on 25 species representing a broad sample of generic and infra generic diversity. A total of 206 phylogenetically informative characters d erived from morphological, chemical, chromosomal, and sequence-based studie s formed the basis for comparative studies. Phylogenetic analysis was used to infer relationships and examine patterns of convergence in key biochemic al and morphological traits associated with dispersal biology. Separate and combined parsimony analyses of three previously unpublished data sets (ITS , chloroplast DNA, morphology/chemistry) supported two major clades, Juglan doideae and Engelhardioideae, in agreement with a recent subfamilial classi fication. Within Engelhardioideae, the genus Engelhardia was found to be pa raphyletic, as E. roxburghiana of the monotypic section Psilocarpeae was re solved as sister taxon to a New World subclade composed of Oreomunnea + Alf aroa. Within Juglandoideae, two tribes are recognized: Platycaryeae and Jug landeae. The monotypic genus Platycarya formed the sister group to Juglande ae, which was resolved fully (Carya-(Juglans-(Cyclocarya + Pterocarpa))). T wo new subtribes, Juglandinae and Caryinae, are described based on the clad istic pattern. Unique morphological apomorphies were detected for all gener a, including the previously little-studied Cyclocarya, which was also deter mined to possess a novel base chromosome number for the family (N = 28). Th e nested position of Annamocarya sinensis within Old World Carya, combined with its lack of unique apomorphies suggested sectional recognition within Carya might be more appropriate for this taxon. Phylogenetic context was us ed to interpret patterns of morphological and chemical variation associated with the evolution of seed dispersal and the tropical versus temperate hab itat. Although the syndrome of wind dispersal appears to be ancestral withi n the family, four novel origins of wing tissue are represented by Engelhar dia/Oreomunnea, Platycarya, Pterocarya, and Cyclocarya. The convergence on animal dispersal has been achieved through three different developmental pa thways in the production of a husk in Alfaroa, Carya, and Juglans. In gener al, wind-dispersed seeds have epigeal germination and those that are animal -dispersed are hypogeous, but Oreomunnea and Cyclocarya are exceptions in t heir respective clades by having wind-dispersed seeds with hypogeal germina tion. The seed-energy reserves are also revealing. With the exception of Or eommunea, wind-dispersed seeds have relatively high concentrations of the u nsaturated linolenic (C) and linoleic (B) fatty acids (CB pattern), whereas all animal-dispersed fruits (viz., Alfaroa, Carya, and Juglans), and Oreom unnea, have relatively high concentrations of the unsaturated oleic (A) and linoleic (B) fatty acids (BA or AB pattern). Tropical genera, whether wind - or animal-dispersed (viz., Oreomunnea, Alfaroa, Annamocarya), have relati vely high concentrations of the saturated palmitic fatty acid. Conversely, wind- and animal-dispersed fruits of temperate genera (viz., Carya, Juglans , Cyclocarya, Pterocarya, and Platycarya) have relatively low percentages o f palmitic acid. The explanation here is based on the fact that seed fats m ust be fluid at the temperature of the living plant, thus selecting for sat urated fats in warm tropical climates and unsaturated lipids in cool temper ate climates.