Weedy Habit Research Articles

A Revision of <I>Solanum</I> Section <I>Lathyrocarpum</I> (the Carolinense Clade, Solanaceae)

Abstract A new taxonomic circumscription of Solanum section Lathyrocarpum is proposed to include 11 species from North and South America. The section is placed in the cosmopolitan S. subgenus Leptostemonum, which contains 350–450 species. As defined here, S. sect. Lathyrocarpum includes all the taxa resolved in the Carolinense clade in previous molecular phylogenetic studies as well as one species not sampled in those analyses. The combination of morphological characters that define the group includes: herbaceous perennial habit with extensive root systems, often with endogenous buds that can sprout, a sparse to dense indumentum of sessile to stalked stellate hairs and tapered prickles, 2- to 3-foliate to plurifoliate sympodial units, extra-axillary inflorescences with 1–20 flowers, a weakly andromonoecious reproductive system, corollas ranging in color from white to lavender, and fruits maturing to yellow or yellowish-orange. Most species in the section have a weedy habit and grow in highly disturbed are...

Functional Trait Differences Between Weedy And Non-Weedy Plants In Southern California

Weedy plants may have unique functional traits that distinguish them from other species. We categorized four annual plant species as weedy and five as non-weedy based on their prevalence in disturbed and invaded environments. This designation was tested in a field trial where we scattered equal numbers of viable seeds in 20 different plots and monitored density and cover over three months. The plants a priori designated as weedy had significantly greater cover and densities than species designated as non-weedy. We hypothesized that a suite of functional traits would define the weedy plant habit. We tested this hypothesis by comparing functional traits between weedy and non-weedy plant species. A principal components analysis (PCA) identified three distinct ecological clusters among the analyzed species (weedy forbs, non-weedy forbs, and grasses). The weedy habit was different from the non-weedy habit in several traits (slower growth, heavier diaspores, earlier flowering initiation, and dormant seeds requiring cold-stratification for germination). Weedy annuals in southern California appear to share a suite of traits, suggesting that their success as weeds is linked to adaptive traits. Further understanding of the traits shared among weedy plant species may help screen for native plants that are valuable for ecological restoration of highly invaded landscapes.

English

Emex spinosus L. (Family Polygonaceae), a decumbent, branched annual herb, was assayed for its allelopathic potential because of it weedy habit. Aqueous extracts were obtained from powdered shoots and leaves at room temperature and by boiling. Various extracts significantly inhibited the germination and seedling growth of Triticum aestivum and Brassica compestris used as test species. The extracts reduced the development of cells and retarded cell division in root tip. Results revealed that the E. spinosus L. has a strong allelopathic potential at least against tested species. The phytotoxicity depended upon the test species and concentration of extract.   Key words: Inhibition, aqueous extract, litter, mulching, Emex allelopathy.

Leaf economic traits from fossils support a weedy habit for early angiosperms

Many key aspects of early angiosperms are poorly known, including their ecophysiology and associated habitats. Evidence for fast-growing, weedy angiosperms comes from the Early Cretaceous Potomac Group, where angiosperm fossils, some of them putative herbs, are found in riparian depositional settings. However, inferences of growth rate from sedimentology and growth habit are somewhat indirect; also, the geographic extent of a weedy habit in early angiosperms is poorly constrained. Using a power law between petiole width and leaf mass, we estimated the leaf mass per area (LMA) of species from three Albian (110-105 Ma) fossil floras from North America (Winthrop Formation, Patapsco Formation of the Potomac Group, and the Aspen Shale). All LMAs for angiosperm species are low (<125 g/m(2); mean = 76 g/m(2)) but are high for gymnosperm species (>240 g/m(2); mean = 291 g/m(2)). On the basis of extant relationships between LMA and other leaf economic traits such as photosynthetic rate and leaf lifespan, we conclude that these Early Cretaceous landscapes were populated with weedy angiosperms with short-lived leaves (<12 mo). The unrivalled capacity for fast growth observed today in many angiosperms was in place by no later than the Albian and likely played an important role in their subsequent ecological success.

An assessment and impact of three invasive species in the Shivalik hills of Himachal Pradesh, India

The Shivalik hills in Northwestern Himalayan range of India have a rich floral diversity. Unfortunately during the last two decades there has been drastic reduction in the diversity of the natural vegetation. The available niches have been occupied by invasive exotic species that were either introduced or have entered accidently. It has resulted from a numbers of factors including increased inter and intra-continental links, import-export and climate change. These exotic species possess certain traits that provide them competitive advantage over the natives and thus aid in their fast spread in the alien environment. Even some of the plants introduced for beneficial purposes have acquired weedy habit. It has greatly altered the structure of the natural ecosystems and caused a dramatic shift in the diversity and dynamics of native flora. The situation has further aggravated due to lack of awareness, insufficient information on the species and its dimensions of the spread besides wide ecological amplitude. It was observed that the diversity, evenness and richness of the native species were drastically reduced in the forest invaded by the exotics. Key words: Northwestern Himalayan, Shivalik hills, invasive, diversity.

Host Range and Selectivity of the Hemiparasitic Plant Thesium chinense (Santalaceae)

Thesium chinense is a hemiparasitic plant that is common in grassland habitats of eastern Asia. Although the physiology of Thesium has been well studied in attempts to control its weedy habit, there have been few ecological investigations of its parasitic life history. Thesium chinense is thought to parasitize species of Poaceae, but evidence remains circumstantial. A vegetation survey was conducted to test whether any plant species occurs significantly more often in plots with T. chinense than expected. In addition, haustorial connections were examined directly by excavating the roots and post-attachment host selectivity was evaluated by comparing the observed numbers of haustoria on different hosts against those expected according to the relative below-ground biomass. Haustorium sizes were also compared among host species. Only two of the 38 species recorded, Lespedeza juncea and Eragrostis curvula, occurred more often in plots with Thesium than expected. In contrast to this, T. chinense parasitized 22 plant species in 11 families, corresponding to 57.9 % of plant species found at the study site. Haustoria were non-randomly distributed among host species, suggesting that there is some post-attachment host selectivity. Thesium chinense generally preferred the Poaceae, although haustoria formed on the Fabaceae were larger than those on other hosts. This is the first quantitative investigation of the host range and selectivity of hemiparasitic plants of the Santalales. The preference for Fabaceae as hosts may be linked to the greater nutrient availability in these nitrogen-fixing plants.

Movement patterns ofRhyssomatus lineaticollisSay (Coleoptera: Curculionidae) within and amongAsclepias syriaca(Asclepiadaceae) patches in a fragmented landscape

Abstract. 1. Dispersal capabilities of organisms are critical in determining the landscape population structure of species as well as their likelihood of survival in fragmented landscapes. Using mark–recapture techniques on the monophagous weevilRhyssomatus lineaticollisSay (Curculionidae), within‐ and between‐patch dispersal capabilities, landscape level population structure, and the role of beetle density and host patch characteristics in setting distances, amounts, and timing of dispersal were studied.2. The data indicate thatR. lineaticollisis sedentary, with 50% of recaptured beetles moving &lt; 1 m and the maximum distance moved &lt; 1 km. Within‐ and between‐patch movement of beetles was unrelated to host plant patch characteristics and beetle densities.3. Despite limited dispersal,R. lineaticollisprobably functions as a patchy population in east‐central Iowa, U.S.A. because dispersals between patches are common and because all host patches surveyed contained this herbivore, indicating a lack of suitable vacant patches, a prerequisite for metapopulation structure.4. Between‐patch distances are well within the dispersal capabilities ofR. lineaticollis, although this may be the result of an increase in the density of patches of its host,Asclepias syriaca, in the landscape over the last 150 years as a result of human disturbance and this species' weedy habit.5. Metapopulation structure in monophagous prairie herbivores may be most likely in species whose non‐weedy host plants form highly predictable resources in space and time, but which are now widely scattered in habitat fragments.

The importance of sexual and asexual reproduction in the recent evolution of Allium vineale.

In the weedy plant species Allium vineale (wild garlic), individuals may simultaneously produce sexually and asexually derived offspring, by seed and bulbils, respectively. In this study, genetic and genotypic diversity was determined in samples from 14 European A. vineale populations using nuclear (RAPD) and cytoplasmic (PCR-RFLP of cpDNA) markers to investigate the importance of the different reproductive modes. In the whole sample, 77 nuclear multilocus genotypes and four chloroplast haplotypes (chlorotypes) were found. Populations exhibited a high degree of subdivision for nuclear and cytoplasmic markers as estimated from hierarchical F-statistics; at the same time, identical chlorotypes could be found in populations separated by large distances. Genotypic diversity was significantly lower than expected under free recombination in almost all populations, indicating that recruitment into populations is mostly by asexually produced offspring. Nevertheless, within each chlorotype, the distribution of markers from pairs of nuclear loci was incompatible with a purely clonal structure, suggesting that many multilocus genotypes have originated by sexual recombination rather than by mutation within asexual lineages. It is argued that the weedy habit of A. vineale is likely to have favored bulbil reproduction, whereas sexually generated genotypes may have facilitated local adaptation during the species' expansion across Europe.

Mimicry of lentil and the domestication of common vetch and grass pea

A hypothesis is proposed whereby weedy vetch (Vicia sativa L.) seed moved with seed of the cultivated lentil (Lens culinaris Medikus) as a tolerated weed during the spread of the lentil from the Fertile Crescent in the Near East to its current distribution. As a result, selection occurred in vetch weeds for a reduction in dormancy/hard-seededness, increased competitive ability and biomass, and phenological adaptation to new environments⇆redisposing the weed for domestication. The cropping of common vetch for forage in pure culture followed. Archaeological evidence of admixtures of grass pea (Lathyrus sativus L.) in Neolithic finds of lentil, pea (Pisum sativum L.) and bitter vetch (Vicia ervilia (L.) Wild.) suggests a similar process of selection in grass pea for a weedy habit from which domestication later occurred.

The evolution of self-fertility inCrepis tectorum (Asteraceae)

The extent of self-fertility was examined in 16 populations ofCrepis tectorum. A hypothesis that a weedy habit favours autogamy was only partly supported. Low levels of self-fertility characterized non-weedy populations from calcareous grasslands (“alvars”) on the Baltic island in Oland. By contrast, plants in nearly all weed populations studied were more or less self-fertile. However, the trend towards autogamy may have occurred independently of the trend towards a weedy habit, as shown by moderately to high levels of self-fertility in alvar populations from two other Baltic islands. In the weed group, there was a tendency for plants from two field populations to be more autogamous than plants from more “ruderal” habitats. There was an association between self-fertility and small, inconspicious heads in the alvar group but the association was weaker when weed populations were also considered. The relatively wide heads characterizing the ruderal weed populations may, at least partly, be an indirect effect of increases in overall plant size and/or in the size of the fruit associated with each flower.

The genus Calceolaria in NW South America. VI. The sections Urticopsis, Lobatae and Micranthera

Three sections of Calceolaria (Scrophulariaceae) in NW South America are revised, viz. sect. Urticopsis (8 species in the area), Lobatae (4), and Micranthera (2). Sect. Urticopsis is characterized by herbaceous, ovate, petiolate leaves and white to buffish pubescence. Sect. Lobatae is characterized by lobate, petiolate leaves and white to greyish white pubescence. Sect. Micranthera comprises small herbs with a weedy habit, characterized by small anthers and unusually long filaments. Three new species are described, viz. C. obtusa, C. trichanthera, and C. adenocalyx (all in sect. Urticopsis), and one new combination is made, viz. C. penlandii ssp. puraceensis (sect. Urticopsis). Chromosome numbers (all 2n = 36) are reported for C. lamiifolia, C. obtusa, C. penlandii ssp. penlandii, and C. dichotoma.

A Preliminary Note on Pollination in the Chenopodiaceae

Somewhat understandably, interest in pollination biology of members of the Chenopodiaceae has been scant (see Percival, 1965, who made no mention of the family), or else has focused on the allergic reaction caused by some members of the family (see Homan, 1963, discussion of Chenopodium album as a secondary factor during the ragweed season). Mode of pollination in chenopods is, we believe, open to question in many instances. The general supposition has apparently been that the family is more or less uniformly anemophilous (e.g., Wodehouse, 1935, 1945, 1971), this in association with an abundant, weedy habit. In accordance, Proctor and Yeo (1972) alluded to the significant presence of chenopodiaceous in the pollen rain. Perhaps the general impression is that chenopods are simply uninteresting in terms of pollination biology. However, if some literature is retraced, a rather different perspective may be gained. Volkens (1893) offered the proposition that most members of the family may actually be entomophilous. Knuth (1909) presented what remains as probably the most detailed account of pollination in the Chenopodiaceae, not to mention a number of other families. From his work one is left with the understanding that chenopods are generally either anemophilous or self-pollinated; however, Knuth did not exclude the possibility of insect visits to such taxa as Salsola kali L. More recently, Ponomarev and Lykova (1960) credited M. Iljin with the suggestion that entomophily is characteristic of the subfamily Spirolobeae (=Salsoloideae, cf. Blackwell, 1977), admitting, however, that the situation had not been adequately studied. Ponomarev and Lykova further credited Z. P. Bochantseva and T. Vitovich with establishing self-pollination in several taxa of chenopods, including certain species of Salsola in Asiatic desert-steppe areas. Ponomarev and Lykova themselves reported the existence of cleistogamy in Petrosimonia triandra (Pallas) Simonk and Salsola brachiata Pallas. However, they stated that cleistogamous flowers were actually no different structurally from chasmogamous ones, but rather, that the stamens in cleistogamous flowers simply did not become exserted (and consequently would shed internally within the flower). They believed that cleistogamy could be quantified (on a percentage basis) merely by counting the number of flowers with included versus exserted stamens. From the preceding brief account, it is obvious that pollination biology in the Chenopodiaceae is much in need of investigation, or reinvestigation as the case may be. Such studies might well result in views of pollination mechanisms in the family substantially different from those currently held. Whereas it is probably true that certain major segments of the family, e.g., a number of species of Atriplex, are predominantly wind-pollinated systems, anemophily may in fact not prove to be the overpowering rule for the Chenopodiaceae as a whole. Entomophily unquestionably plays a role in some genera. Although entomophily may