No abstract

Despite much recent activity in the phylogeny and developmental genetics of grasses, the enigmatic homologies of their reproductive structures remain largely unresolved, partly because their highly derived morphology has resulted in a unique associated terminology. Outstanding questions include whether grass lodicules and stamens are derived from a single perianth or stamen whorl, respectively, whether the grass caryopsis is homologous with a nut, and how the scutellum evolved. We investigated the reproductive structures of the putative sister group of grasses, the southwestern Australian family Ecdeiocoleaceae, which includes two genera, Ecdeiocolea and Georgeantha. The zygomorphic arrangement of the four (rather than six) stamens in male flowers of Ecdeiocolea indicates that they may represent three outer stamens plus the adaxial inner stamen. Within Ecdeiocoleaceae, characters such as the highly unusual nucellus structure of Ecdeiocolea are autapomorphic. Sister-group comparisons indicate that some characteristic grass features, notably the scutellum, do not occur in their putative closest relatives and that more data are needed on early-diverging grass genera to resolve these issues. The grass caryopsis could represent one end of a transformation series embodied by the reduced gynoecial structure and indehiscent fruit of other Poales such as Flagellaria, Joinvillea, and Ecdeiocolea.

No abstract

A UK seed conservation collection of Anemone nemorosa L. seeds held at the Millennium Seed Bank (MSB) showed low viability in its first poststorage test. Because achenes of A. nemorosa are naturally dispersed when they are green, we tested the hypothesis that seeds may not be fully desiccation tolerant and storable at the time of natural dispersal, and that a post-harvest treatment could increase the proportion of desiccation-tolerant seeds. Achenes harvested at the point of natural dispersal in late May in 2003 and 2004 were either placed immediately on 1% water agar at 208C ('laboratory' treatment), or placed in nylon sachets and buried in leaf litter among plants growing in the wild ('field' treatment). Samples were withdrawn at intervals over a period of 168 d and tested for desiccation tolerance (drying to 0.059 g H 2 O (g DW) 21 ) and longevity (controlled ageing at 60% relative humidity and 458C). An initial increase, followed by a decline, in the proportion of seeds surviving desiccation and in the longevity of both laboratory-and field-treated samples coincided with the development of embryos from globular to heartand then torpedo-shaped. Developmental arrest was not required for the acquisition of desiccation tolerance, and continued growth and development of the embryo resulted in a loss of desiccation tolerance, similar to that seen in orthodox seeds upon radicle emergence. Furthermore, while A. nemorosa seeds, like many from the Ranunculaceae family, might be described as having morphological or morphophysiological dormancy, this lack of developmental arrest does not fit with the usual concept of dormancy. The implications of these results for the classification systems of seed-storage behaviour and dormancy, and for the long-term conservation of seeds of A. nemorosa, are discussed.

Desiccation-sensitive recalcitrant seeds and fruits are killed by the loss of even moderate quantities of water. Consequently, minimizing the rate of water loss may be an important ecological factor and evolutionary driver by reducing the risk of mortality during post-dispersal dry-spells. For recalcitrant fruits of a range of Quercus species, prolonged drying times have been observed previously. However, the underlying mechanism(s) for this variation is unknown. Using nine Quercus species we investigated the major route(s) of water flow into and out of the fruits and analysed the relative importance of the different pericarp components and their anatomy on water uptake/loss. During imbibition (rehydration), the surface area of the cupule scar and the frequency and area of the vascular bundles contained therein were significantly correlated with the rates of water uptake across the scar. The vascular bundles serving the apex of the fruit were a minor contributor to overall water. Further, the rate of water uptake across the remainder of the pericarp surface was significantly correlated with the thickness of the vascularised inner layer in the pericarp. Fruits of Q. franchetii and Q. schottkyana dried most slowly and had a comparatively small scar surface area with few vascular bundles per unit area. These species inhabit drier regions than the other species studied, suggesting these anatomical features may have ecological value by reducing the risk of desiccation stress. However, this remains to be tested in the field.