Cortical development in roots of the aquatic plant Pontederia cordata (Pontederiaceae)

Adventitious roots of marsh-grown Pontederia cordata were examined to determine cortical development and structure. The innermost layer of the ground meristem forms the endodermis and aerenchymatous cortex. The outermost layer of the early ground meristem undergoes a precise pattern of oblique and periclinal cell divisions to produce a single or double layer of prohypodermis with an anchor cell for each radial file of aerenchyma cells. At maturity, endodermal cell walls are modified only by narrow Casparian bands. The central regions of the ground meristem become proaerenchyma and exhibit asymmetric cell division and expansion. They produce an aerenchymatous zone with barrel-shaped large cells and irregularly shaped small cells traversing the aerenchyma horizontally along radii; some crystalliferous cells with raphides are present in the aerenchyma. The walls of the hypodermis are modified early by polyphenols. The outermost layer of the hypodermis later matures into an exodermis with Casparian bands that are impermeable to berberine, an apoplastic tracer dye. The nonexodermal layer(s) of the hypodermis has suberin-modified walls. Radial files of aerenchyma are usually connected by narrow protuberances near their midpoints, the aerenchyma lacunae having been produced by expansion of cells along walls lining intercellular spaces. We are terming this type of aerenchyma development, which is neither schizogenous nor lysigenous, "differential expansion."     

Biological control of waterhyacinth in Sinaloa Mexico with the weevils Neochetina eichhorniae and N. bruchi

Water hyacinth (Eichhornia crassipes (Mart.) Solms.)creates severe problems in the irrigationdistricts of Mexico, particularly in westernSinaloa. Therefore water hyacinth weevils(Neochetina eichhorniae Warner and N. bruchi Hustache), imported from the USA in1993, were used to initiate a biologicalcontrol program. Precautionary screeningrevealed that some were infected with amicrosporidian so disease-free colonies wereproduced by eliminating infected breedinglines. To demonstrate effectiveness prior toopen field releases, weevils were firstreleased in cages at field sites. Weevilintensity increased to 6.3 weevils/plant after320 days when the plants were all dead ordying. More than 8,600 N. bruchi and14,500 N. eichhorniae were then releasedat various sites during January 1995 to August1996. Waterhyacinth coverage declined atBatamote reservoir (134 ha) from 95% to <3%by 1997; at the 12-ha Hilda reservoir from100% in May 1995 to 1% by March 1998; at the42.3-ha Arroyo Prieto reservoir from 100% to1% during the same interval; and at theMariquita reservoir (492 ha), the largestreservoir in the Humaya system, from 394 ha(80%)to 98.4 ha (20%).     

Taxonomic revision of Melanocyphus Jekel (Coleoptera: Curculionidae)

Cornops aquaticum (Bruner) is host specific on Eichhornia spp. and Pontederia spp. (Pontederiacae). Its present distribution ranges from Mexico to Argentina. The number of juvenile instars (5-7) apparently mirrors the photoperiod and temperature pulses of different climatical conditions in the respective geographical regions. Based on life-history data, three working hypotheses are proposed for forthcoming studies. These will test whether the varying number of juvenile instars represents a phenotypic plasticity of a single genotype or an adaptation that is genetically fixed, due to an evolutionary relationship of the host with its host-plant.     

CONTRIBUTION OF CRYPTIC INCOMPATIBILITY TO THE MATING SYSTEM OF EICHHORNIA PANICULA TA (PONTEDERIACEAE)

Tristylous populations of the annual aquatic Eichhornia paniculata have high levels of outcrossing and intermorph mating despite being fully self- and intramorph compatible. Experimental studies of pollen germination, ???pollen-tube growth, and pollinations with mixtures of genetically marked pollen were used to determine whether postpollination processes contribute to the observed mating patterns. Differences in pollen germination were small and did not contribute to differences in pollen siring ability. The fraction of pollen tubes first entering the ovary, however, was greater for legitimate outcross pollen than for either of the other two pollen types (self or outcross illegitimate pollen) in all recipient morphs. Moreover, legitimate pollen had higher siring success when in competition with illegitimate pollen types (self or outcross) in each recipient style morph. The ranking of pollen performance for different pollen-style combinations was the same for both the pollen-tube growth and marker-gene experiments indicating that differences in pollen-tube growth rate are the principal cause of differences in pollen siring ability. Cryptic incompatibility in E. paniculata may represent a weak heteromorphic incompatibility system because the observed patterns of pollen-tube growth parallel pollen-tube growth and seed-set patterns that occur in related species with strong trimorphic incompatibility. The ability to produce mostly outcrossed progeny when pollinators are abundant, but to reliably produce seed under a variety of environmental and demographic conditions may be favored in E. paniculata because of its colonizing life history and occurrence in ephemeral habitats. Cryptic incompatibility may be more likely to occur in species subject to wide fluctuations in population size and levels of pollinator service.     

RECONSTRUCTION OF THE EVOLUTION OF REPRODUCTIVE CHARACTERS IN PONTEDERIACEAE USING PHYLOGENETIC EVIDENCE FROM CHLOROPLAST DNA RESTRICTION-SITE VARIATION

We reconstructed the phylogenetic history of Pontederiaceae using chloroplast DNA restriction-site variation from approximately two-thirds of the species in this family of aquatic monocotyledons. The molecular phylogeny was used to evaluate hypotheses concerning the evolution of reproductive characters associated with the breeding system. The family has four main genera, two of which (Eichhornia and Pontederia) have tristylous, predominantly outcrossing species, while two (Monochoria and Heteranthera) have enantiostylous taxa. Self-incompatibility is restricted to some but not all tristylous species. In Eichhornia and Pontederia, predominantly selfing species with small monomorphic flowers (homostyly) have been hypothesized to result from the multiple breakdown of tristyly. Restriction-site variation provided a well supported phylogeny of ingroup taxa, enabling the mapping of reproductive characters onto trees. Two contrasting optimization schemes were assessed, differing in the relative weights assigned to shifts in character states. The reconstructed sequence of floral character-state change was used to assess competing hypotheses concerning the origin and breakdown of tristyly, and the relationships between tristylous and enantiostylous syndromes. Our results indicate that the class of optimization scheme used was the most critical factor in reconstructing character evolution. Despite some topological uncertainties and difficulty in reconstructing the primitive floral form in the family, several broad conclusions were possible when an unordered, unequally-weighted optimization scheme was used: (1) tristyly originated either once or twice, while the occurrence of enantiostyly in Monochoria and Heteranthera was always found to have independent origins; (2) tristyly has repeatedly broken down leading to selfing, homostylous taxa; and (3) self-incompatibility probably arose after the origin of floral trimorphism, a sequence of events that conflicts with some evolutionary models.     

Structural features of a polysaccharide from the mucin of water hyacinth

The mucin found in the nodal region of the weed, water hyacinth (Eichhornia crassipes), is a heteropolysaccharide composed of d-xylose, l-galactose and l-arabinose in the mol ratio of 1.3:1.2:1.0. Partial hydrolysis with acid gave four oligosaccharides which were characterized as: d-Xylp-(1 → 3)-l-Ara, l-Galp-(1 -→ 2)-l-Ara, d-Xylp-(1 → 3)-l-Galp-(1 → 2)-l-Ara, and d-Xylp-(1 → 2)-d-Xylp-(1 → 3)-l-Galp-(1 → 2)-l-Ara. These, together with the results of methylation analysis using GC and GC/MS and periodate oxidation, indicated that the trisaccharide repeating unit, → 4)-d-Xylp-(1 → 3)-l-Galp-(1 → 2)-l-Araf-(1 →, constitutes the backbone of the polysaccharide. Further, all the d-xylopyranosyl residues of the backbone are substituted at O-2 and, in addition, one out of seven such residues is also substituted at O-3; the substituents being l-Araf-(1 →, d-Xylp-(1 →, l-Galp-(1 →, d-Xylp-(1 → 3)-l-Araf-(1 →, residues.     

Monochoria vaginalis var. angustifolia，a new variety of the Pontederiaceae from Thailand

A new variety of Monochoria C. Presl from Thailand, M. vaginalis （N. L. Burman）Kunth var.angustifolia G. X. Wang, is described. This variety can be distinguished from the typical one, M. vaginalis var. vaginalis, by having mature leaves narrowly lanceolat     

Variation in daily floral display and the potential for geitonogamous pollination in two monomorphic enantiostylous Monochoria species

Mirror-image flowers (enantiostyly) have long been considered a mechanism to promote cross-pollination between flowers of alternate stylar orientation. However, in monomorphic enantiostyly, the occurrence of both left- and right-styled flowers on the same individual plant might appear to promote geitonogamy rather than outcrossing relative to the condition of dimorphic enantiostyly. We investigated daily floral display during the flowering season in two experimental populations of monomorphic enantiostylous species, Monochoria korsakowii and Monochoria vaginalis (Pontederiaceae) to assess the potential effects of floral display on geitonogamous pollination. The left- and right-styled flowers exhibited a 1:1 ratio both within individuals and populations. In M. korsakowii and M. vaginalis, 86.0% and 71.3% daily floral displays involved fewer than three flowers thus reducing the likelihood of geitonogamy. Moreover, daily displays often involved one floral form and mixed-formed with unequal ratios of left- and right-styled flowers also reducing opportunities for geitonogamy. Therefore variation in daily floral display in these two Monochoria species suggests that the impact of monomorphic enantiostyly in promoting geitonogamy will be reduced by small display sizes, or through simulating dimorphic enantiostyly.     

泰国雨久花属（雨久花科）一新变种——窄叶鸭舌草

描述了泰国雨久花属Monochoria C.Presl一新变种:窄叶鸭舌草M.vaginalis var.angustifolia G.X.Wang。该新变种与原变种鸭舌草M.vaginalis var.vaginalis都具有类似的总状花序,但前者的叶片为窄披针形,3-7×0.3-2.0cm,叶片宽长比在0.1-0.4之间,叶基部裂片最长不超过2mm,总状花序具花3-7朵,而原变种鸭舌草的叶片较宽,为卵心形或心形,4-9×2-8cm,叶片宽长比在0.5-0.95之间,叶基部裂片最长可达到2cm,总状花序     

The Host Range ofEccritotarsus catarinensis(Heteroptera: Miridae), a Potential Agent for the Biological Control of Waterhyacinth (Eichhornia crassipes)

The host range ofEccritotarsus catarinensiswas determined using 33 plant species to assess the risk of using this insect, a native of South America, for the classical biological control of waterhyacinth (Eichhornia crassipes) in Australia and Papua New Guinea. The results, in conjunction with the results of Hillet al.(1999) who tested 67 species (mostly South African), strongly suggest thatE. catarinensisis restricted to the Pontederiaceae, a family of aquatic plants. All five species of Pontederiaceae in the Australian testing,E. crassipes, Pontederia cordata, Monochoria vaginalis, M. cyanea,andM. australasica,were suitable for insect development. Colonies persisted for at least four generations onE. crassipes, P. cordata,andM. vaginalis.Two-way choice and multiple-choice preference trials were conducted and discussed.E. catarinensisdid not exhibit a clear preference for waterhyacinth over other Pontederiaceae in these trials. Most oviposition occurred into the upper surface of the lamina during laboratory testing despite observations that the underside was preferred in the field. Although not considered suitable for release in Australia, this insect may be useful in other countries where more serious waterhyacinth problems occur and whereM. vaginalisis a serious weed, such as in Southeast Asia.