Steps Toward the Natural System of the Dicotyledons

The value of vegetative anatomy in phylogenetic analysis is documented. Examples of the use of vegetative anatomy at different taxonomic levels show the continuing role of the anatomical method in building a more natural system of classification of the dicotyledons. The importance of correlating wood and leaf anatomical features with ecological and floristic preferences of taxa is emphasized. Caution is required in basing phylogenetic interpretations upon similarities and differences in xylem structure. The transition from scalariform to simple perforation plates is the only aspect of vessel element evolution that is not potentially reversible and all phylogenetic analyses must reflect this important principle. Some groups outside the Magnoliidae (Annoniflorae) possess very primitive xylems and can be used as evidence to support a pattern of multiple early radiations of the dicotyledons, as well as the increased awareness of a lack of clear subclass definition. The application of anatomical characters in cladistic analysis is reviewed, and the need to utilize strictly homologous features, to provide accurate scoring of character states, and to give proper interpretations to character state transformations is emphasized

Stem and Leaf Anatomy of the Alseuosmiaceae

The stem and leaf anatomy of five species representing all three genera of the small Southwest Pacific dicotyledonous family, Alseuosmiaceae, were studied. Salient anatomical features common to all genera include: a trilacunar, three-trace leaf-node structure in which petioles are supplied with three separate vascular bundles; rosoid teeth bearing hydathodes; anomocytic stomata; unicellular, bicellular, and multicellular, unbranched, living trichomes; a superficial origin of periderm; leafmesophyll composed of a uniseriate palisade region and a loosely constructed spongy zone; and the presence of a stem and foliar endodermis. Sclerenchyma occurs in stem tissues of species belonging to all three genera and Crispiloba disperma contain numerous elongate, filiform or fibrosclereids in the stem, petiole, and leaf mesophyll. Leaves are pinnately veined or, in the case of Wittsteinia vacciniacea, with acrodromous venation. Secondary venation is brochidodromous or semicraspidodromous. As presently constituted the family has a distinctive combination of derived wood and stem anatomical characters, and provides an excellent example of the successful application of vegetative anatomical evidence in solving problems of family relationship and generic affinities. The presence of an endodermis in the aerial organs provides additional support to the suggestion that the family evolved from a small, shrubby ancestor, subsequently became semiherbaceous, followed by the development of a secondarily woody body in some taxa. The totality of anatomical characters reinforces the view that the Alseuosmiaceae have their nearest relatives within the rosalean-saxifragalean complex

The Bases of Angiosperm Phylogeny: Vegetative Anatomy

Volume: 62Start Page: 590End Page: 62

COMPARATIVE MORPHOLOGICAL STUDIES IN DILLENIACEAE, I. WOOD ANATOMY

Volume: 48Start Page: 1End Page: 2

COMPARATIVE MORPHOLOGICAL STUDIES IN DILLENIACEAE, III. THE CARPELS

Volume: 49Start Page: 317End Page: 33