Evolution, phylogeny, and systematics of the Juglandaceae

A comprehensive systematic investigation was conducted on the extant Juglandaceae based on 25 species representing a broad sample of generic and infrageneric diversity. A total of 206 phylogenetically informative characters derived from morphological, chemical, chromosomal, and sequence-based studies formed the basis for comparative studies. Phylogenetic analysis was used to infer relationships and examine patterns of convergence in key biochemical 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 Separate and combined parsimony analyses of three previously unpublished data sets (ITS, chloroplast DNA, morphology/chemistry) supported two major clades, Juglandoideae and Engelhardioideae, in agreement with a recent subfamilial classification. Within Engelhardioideae, the genus Engelhardia was found to be paraphyletic, as E. roxburghiana of the monotypic section Psilocarpeae was resolved as sister taxon to a New World subclade composed of Oreomunnea + Alfaroa. Within Juglandoideae, two tribes are recognized: Platycaryeae and Juglandeae. The monotypic genus Platycarya formed the sister group to Juglandeae, which was resolved fully (Carya-(Juglans-(Cyclocarya + Pterocarpa))). Two new subtribes, Juglandinae and Caryinae, are described based on the cladistic pattern. Unique morphological apomorphies were detected for all genera, including the previously little-studied Cyclocarya, which was also determined to possess a novel base chromosome number for the family (N = 28). The 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 used to interpret patterns of morphological and chemical variation associated with the evolution of seed dispersal and the tropical versus temperate habitat. Although the syndrome of wind dispersal appears to be ancestral within the family, four novel origins of wing tissue are represented by Engelhardia/Oreomunnea, Platycarya, Pterocarya, and Cyclocarya. The convergence on animal dispersal has been achieved through three different developmental pathways in the production of a husk in Alfaroa, Carya, and Juglans. In general, wind-dispersed seeds have epigeal germination and those that are animal-dispersed are hypogeous, but Oreomunnea and Cyclocarya are exceptions in their respective clades by having wind-dispersed seeds with hypogeal germination. The seed-energy reserves are also revealing. With the exception of Oreommunea, wind-dispersed seeds have relatively high concentrations of the unsaturated linolenic (C) and linoleic (B) fatty acids (CB pattern), whereas all animal-dispersed fruits (viz., Alfaroa, Carya, and Juglans), and Oreomunnea, 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 relatively 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 of palmitic acid. The explanation here is based on the fact that seed fats must be fluid at the temperature of the living plant, thus selecting for saturated fats in warm tropical climates and unsaturated lipids in cool temperate climates.