Robert B. Kaul

Morphology of germination and establishment of aquatic seedlings in alismataceae and hydrocharitaceae

Abstract The germination and early growth of seedlings is reported for 4 species of Alismataceae (including Limnocharitaceae) and 2 species of Hydrocharitaceae. The seeds germinate in the achenes of Alisma subcordatum, Echinodorus rostratus, and Lophotocarpus calycinus, and the hypocotyl grows directly from the micropylar end of the seed through the base of the pericarp, which is its weakest part. The recurvate shape of the seed is thus adaptive insofar as the emerging hypocotyl is aimed directly at the easiest point of exit. Most seeds fall from the open, floating follicles of Limnocharis flava but a few germinate within the follicles. The seeds of Vallisneria americana and Ottelia alismoides fall to the bottom from the disintegrating fruits. In all cases, the seedlings are temporarily anchored by hypocotylar hairs which form soon after the hypocotyl emerges. A primary root, if present, forms soon afterward and the first adventitious roots appear when the earliest plumular leaves form.

Anatomical Observations on Floating Leaves

Abstract An examination of 24 genera of aquatic plants having floating leaves and leaf-like thalli has been made. Functional stomata occur on the adaxial sides of floating leaves of angiosperms and some ferns, and in some floating leaves there are stomata on the abaxial surface as well. Most floating leaves have prominently chambered mesophyll, and in some instances the chambers are locally enlarged and form buoys.

The Niobrara River Valley, a Postglacial Migration Corridor and Refugium of Forest Plants and Animals in the Grasslands of Central North America

The Niobrara River Valley of northern Nebraska contains numerous bryophyte, vascular plant, and animal species more typical of forests far to the east, north, and west than to other forests in the grasslands that surround the Valley. Some species are probably relicts of cooler glacial and early postglacial times, when much of what is now grassland was covered by boreal and cool-temperate forests. Others entered the Valley from the east in postglacial times, and some entered from the west as the climate became semi-arid. There is a steep decline in total number of vascular plant species from the mouth of the Missouri River up through the Niobrara Valley, suggesting an environmental gradient and differential migration and extirpation of species at various times since the Pleistocene.AbstraktumDas Niobrara Flusstal nördliches Nebraska enthält viele Laubmoose, Gefässpflanzen, und Tiere Arten, die mehr typisch für ostliche, nördliche, und westliche Wälder sind, als andere Wälder auf der umgebenden Wiesen. Manche Arten sind vielleicht Hinterbliebene von kühleren vergletscherten und frühe nach vergletscheten Zeiten. Andere eintraten ins Tal von Osten während nachvergletscherten Zeiten, und manche eintraten von Westen, während das Klima halb dürr wurde. Es gibt eine steile Neige in die Summe Gefässpflanzenarten von der Mündung des Missouri Fluss bis dem Niobrara Tal, die eine Umgebungsteigung und Unterscheidungswanderung und Ausrottung Arten um verschiedene Zeiten seitdem Pleistozän vorschlagen.ResumenEl Valle del Rio Niobrara, en el norte de Nebraska, contiene un gran número de especies de briofitas, plantas vasculares, y animales que son tipicos de los bosques del este, norte, y oeste de Estado Unidos que de las praderas que rodean al Valle. Alqunas de estas son probablemente vestigios de peridos frios de glaciación y tempranos eventos pos-glaciales, cuando gran parte de lo que es hoy pradera estaba cubierto por bosques boreales y templados. Otras especies entraron al Valle del este en el periodo pos-glacial, y otras entraron del oeste segun el clima se torno semiárido. Hay un alto declive en el número total de plantas vasculares desde le boca del Rio Missouri atravesando el Valle Niobrara, sugiriendo un gradiente ambiental, migración diferencial y extirpación de especies en varias épocas desde el Pleistoceno.

Reproductive phenology and biology in annual and perennial Alismataceae

Abstract Two annual ( Echinodorus rostratus (Nutt.) Engelm., Sagittaria calycina Engelm.) and 3 perennial ( Alisma subcordatum Rat., S. brevirostra Mack & Bush, S. latifolia Wild.) species of Alismataceae were compared to determine differences in reproductive effort and timing. The annuals produce flowers and fruits earlier and later than the perennials and, under optimal conditions, the annuals also produce more (but smaller) seeds annually per plant. Populations of the annuals occur on exposed mud and are erratically abundant from year to year, while populations of the perennials are more stable. Seed viability of the annuals decreases more slowly over time. There is general congruence of these life-history attributes with the concepts of “ r ” and “ K ” strategies.

Foliar and reproductive responses of Sagittaria calycina and Sagittaria brevirostra (Alismataceae) to varying natural conditions

Abstract Contiguous populations of an annual (Sagittaria calycina Engelm.) and a perennial species (Sagittaria brevirostra Mack. & Bush.) showed both similar and different foliar and reproductive responses to dry, wet, and deep-water environments. Both species produced smaller leaves in dry and deep-water conditions than on saturated soil in shallow water; deep-water leaves were much narrower. Both species produced larger, more floriferous inflorescences in wet than in dry conditions, and both were sterile in the deep-water environment. Male flowers outnumbered females in S. brevirostra in dry and wet conditions, but the ratio of males to females was much higher in dry situations. The ratio of male to perfect flowers in S. calycina was low in both environments, but fewer achenes per flower were formed in dry conditions.

Phylogeny of Sparganium (Typhaceae) revisited: non-monophyletic nature of S. emersum sensu lato and resurrection of S. acaule

The diploid aquatic genus Sparganium (Typhaceae) comprises ca. 14 species mainly in cool temperate regions of the world. Among these, S. emersum comprises two infraspecific taxa, subspecies acaule from eastern North America and subspecies emersum from Eurasia and western North America (and occasionally from eastern North America as well). However, there has been some discussion regarding the monophyly of S. emersum sensu lato. We tested the hypothesis of a polyphyletic S. emersum sensu lato in a phylogenetic framework. Sequence data from six plastid DNA regions and nuclear phyC were analyzed using maximum parsimony, maximum likelihood, and Bayesian inference. We obtained a moderately resolved phylogeny with the plastid DNA data set, while phylogenetically less-informative phyC was useful to distinguish morphological species and discern hybrid and non-hybrid specimens. Sparganiumemersum sensu lato was resolved as polyphyletic, clustering with S. angustifolium and S. glomeratum, respectively. Sparganiumacaule is resurrected to be a sister to S. glomeratum, for which synapomorphic and distinguishing morphological characters are provided. Three cases of hybridization were detected.