Raúl Pozner

Changes in Floret Development Patterns That May Correlate with Sex Determination in the PCK Clade (Poaceae)

We investigated changes in floral developmental patterns and sex determination in the PCK (phosphoenolpyruvate carboxykinase) clade using a comparative approach and SEM. We identified variation in patterns of floral development that may be correlated with sex determination. Nine different patterns of floret development were identified, based on sex of the lower floret, sequence of stamen development, and rate of glume and lemma differentiation. Although staminate florets are always formed by the abortion of the gynoecium, the timing of abortion differs among species. Similarly, the formation of sterile lower florets showed different pathways that may operate at the level of floral meristem or organ identity. Finally, we discuss several reasons why patterns described for maize and closely related species may not be easily extrapolated to other grasses.

FLORAL STRUCTURE, ANTHER DEVELOPMENT, AND POLLEN DISPERSAL OF HALOPHYTUM AMEGHINOI (HALOPHYTACEAE)

A developmental and anatomical study of the staminate flowers of Halophytum ameghinoi showed decussate tepal estivation; residual growth of the receptacle after stamen inception; monocotyledonous and basic types of anther wall development; secretory, binucleate tapetal cells; tetrahedral tetrads; and binucleate pollen grains. A vacuolate stage in the archesporial cells, the structure of endothecial thickenings, and a mechanism of anther dehiscence by connective contraction are new autapomorphies for this family. Anemophily is confirmed (Plantago‐type syndrome), and field studies of pollen release showed a subtle mechanism involving rigid anther wall structure, versatile anther insertion, and abaxial subterminal pores. In air currents, while anthers flutter with pores directed upwind, pollen is extracted presumably by a cavitation effect of the hooded anther tip. In a phylogenetic context, anemophily of Halophytum is of isolated occurrence within Caryophyllales, and uniovulate ovaries in sister clades probably represent a prerequisite for evolution of anemophily.

Multiple origins of congested inflorescences in Cyperus s.s. (Cyperaceae): Developmental and structural evidence

PREMISE OF THE STUDYnThe understanding of homoplasic structures becomes more relevant when they are complex and define large angiosperm taxa. Inflorescence architecture usually fulfills both features, as happens with Cyperus, a genus with two taxonomical subdivisions characterized either by alternative expressions of Kranz anatomy (C(3) or C(4)) or inflorescence shape (condensed or lax). Those subdivisions are not completely congruent because at least one of these presumed characters has evolved several times. We focused a SEM study on the inflorescence development in species with condensed inflorescences and different photosynthetic anatomy to test the possibility that condensed inflorescences of subgen. Anosporum (C(3) anatomy) have evolved independently from those of subgen. Cyperus (C(4) anatomy).nnnMETHODSnFreshly collected inflorescences of C. entrerianus, C. eragrostis, C. oxylepis, and C. incomtus were studied using stereoscopic and scanning electron microscopy.nnnKEY RESULTSnCondensed inflorescences of Cyperus species with C(3) and C(4) anatomy had differences in structure and development: (1) mature structure, (2) position of second-order branching initiation in the first developmental stage of the inflorescence, (3) main axis development and elongation, and branching development, (4) types of ramifications, (5) phyllotaxis and symmetry.nnnCONCLUSIONSnResults support multiple origins of condensed inflorescences in Cyperus, based especially on differences in timing during development and elongation of the main axis and branches, branching pattern and phyllotaxis. Structure and development may be the key to using inflorescence morphology as an external feature to distinguish large natural groups within Cyperus based on vegetative anatomy.

Using integrative taxonomy and multispecies coalescent models for phylogeny reconstruction and species delimitation within the “Nastanthus–Gamocarpha” clade (Calyceraceae)

The Calyceraceae (47 spp.) is a small family of plants that is sister to the Asteraceae (∼ 25,000 spp.), one of the largest families of angiosperms. Most members of Calyceraceae are endemic to the Andes and Patagonia, representing an excellent model within which to study diversification patterns in these regions. The single phylogenetic study of Calyceraceae conducted to date revealed that the boundaries of most genera and several species of this family require further analyses, especially the Nastanthus-Gamocarpha clade. In this study, we reconstructed the phylogeny of the Nastanthus-Gamocarpha clade using multispecies coalescent models under BPP and StarBeast2 programs, sampling 63 individuals from 13 of the 14 species recognized to date. We then used this phylogenetic framework to delimit species using BFD and the A11 method implemented in BPP. Species limits suggested through a coalescent approach were then re-evaluated in the light of morphology, geography, and phenology. Coalescent-based methods indicated that most putative lineages could be recognized as distinct species. Morphological, geographical, ecological, and phenological data further supported species delimitation. Necessary taxonomic changes are proposed. Namely, the paraphyletic Nastanthus is synonymized under Gamocarpha, while five species of Boopis are transferred into Gamocarpha. We used an integrative taxonomic approach to recognize 13 species and one subspecies within the newly circumscribed genus Gamocarpha.

A New Species of Mastigostyla (Iridaceae) from Argentina

Abstract We describe and illustrate Mastigostyla coronata, a new species of Iridaceae from the high Andes of Jujuy (Argentina), morphologically similar to Mastigostyla vargasii. The inclusion of this new species in Mastigostyla is supported by a phylogenetic analysis based on plastid markers. We also present a morphological comparison among the sub-acaulescent species of Mastigostyla (including Cardenanthus), and a key to those species.