Hypochaeris Glabra Research Articles

Responses of Annual Vegetation to Temperature and Rainfall Patterns in Northern California

Weather patterns significantly influence annual vegetation, both within and between years. The impact of these weather patterns on standing crop, cover, and botanical composition were investigated during the years 1955—1973 inclusive. Standing crop increased as the growing season progressed from March to June, while cover declined. Erodium spp. Carduus pycnocephalus, Geranium spp. and Hypochoeris glabra all declined between these 2 calendar dates. Other annual species increased in botanical composition as the growing season progressed. Weather patterns primarily influenced total standing crop during the initial period of plant growth. Following germination, temperatures were typically warm and conducive to plant growth; drought at this time suppressed total standing crop. Consistent precipitation following fall germination, and again during the period of rapid plant growth in spring, contributes to a "grass year" in the annual type. The sequence of freezing temperatures in relation to phenology of developing grass seedlings determines the relative proportion of annual grass species from one year to the next. Botanical composition of Trifolium spp. and Medicago hispida depends upon mild autumn weather, particularly when such fall weather favors none of the annual grass species. Botanical composition of Erodium spp. positively correlated with weather patterns associated with dry fall conditions. Multiple regressions of standing crop on weather patterns produced useful guidelines for manipulating animal units to achieve complete utilization of available forage, particularly when these equations were implemented in seasonal stages.

Toxicity of Artemisia californica to Four Associated Herb Species

Natural and artificial rain drip, soil and leaf volatiles from Artemisia californica are toxic to Hypochoeris glabra and Madia sativa but not nearly as toxic to Bromus rigidus and Festuca megalura. This supports the hypothesis, based on distributional patterns and animal exclosure experiments, that the former two species are allelopathically excluded from thickets of A. californica, but that the latter two are not. Volatile toxins are adsorbed by the soil during the dry season and released into the soil solution with the first rains. Toxins also come from litterfall and rain drip. Toxicity exists only at the very beginning of the wet season, after which the soil, leaves and rain drip become relatively innocuous.

Aneuploidy and isolation in two Hypochoeris species

The annual species Hypochoeris glabra (2n = 10) and the perennial H. radicata (2n = 8) hybridise readily in nature and in experiment. During meiosis in F1 hybrids the maximum association is a chain of seven and a bivalent indicating that at least three interchanges differentiate the two genomes. The nucleolar chromosomes in the two species are homologous and form a ring bivalent. They are, however, differentiated since in the F1 hybrid only one nucleolar-organiser region is expressed. Although chromosomal differentiation reduces the egg fertility of F1 hybrids to about 1%, viable backcross hybrids to H. radicata as pollen parent have been experimentally produced and occur in natural populations. Backcrosses with 8, 9 and rarely 13 chromosomes are found and those with 2n = 8 are fully interfertile with H. radicata. Gene flow may therefore take place in natural populations across an aneuploid barrier. The direction of gene flow in Hypochoeris is probably unidirectional from the annual to the perennial.

Angiosperm Parasite and Host: Coordinated Dispersal

Seeds of the root parasite Orthocarpus densiflorus may be dispersed by the propagules of its host, Hypochoeris glabra. Such coordinated transport, which includes seed clustering, reinforces the integration and stability of populations of this host and parasite.

The effect of phosphate supply on the growth and botanical composition of annual type pasture

The results of two long-term field experiments and two 1-year experiments are reported. In three of these, severe phosphate deficiency was present initially. At high phosphate supply, the annual total yield was not significantly related to age of pasture over periods of 10–13 years. At intermediate and low supply, yields relative to high phosphate supply increased significantly with time; these increases are believed to demonstrate residual effects of phosphate. Indirect evidence for nitrogen accretion from clover under severely phosphate-deficient conditions is presented. Sward components—in the long term—responded differentially to phosphate supply. With very low phosphate, erodium (Erodium botrys (Cav.) Bertol.) and flatweed (Hypochoeris glabra L.) were dominant; whereas with high phosphate, cape-weed (Cryptostemma calendula (L.) Druce) and ripgut brome grass (Bromus rigidus Roth)—or else barley grass (Hordeum leporinum Link)—were dominant. Subterranean clover (Trifolium subterraneum L.), though present under these extremes, was relatively more plentiful at intermediate levels of supply. However, at "steady state" conditions, the range in clover content was fairly narrow (from c. 20 to 40%). The significance of these findings to a sheep infertility problem ("clover disease") of subterranean clover-dominant pastures is discussed.

The Return of Native Perennial Bunchgrass Following the Removal of Klamath Weed (Hypericum Perforatum L.) by Imported Beetles

During the relatively short period of 4 years since release of imported beetles which feed on it, Klamath weed, HypericUri perforatiun, a serious weed on perhaps a million or more acres of Western range lands, has been brought under strikingly successful control in limited areas by this tool of applied ecology. Though the range in queston has not yet been put under normal grazing, the rapidity and vigor with which the climax hunchgrass, Dantho nia californica, entered the space vacated by the removal of Klamath weed by beetles of the genus Chrysomuiela (= Chrysolina), promises much for the more favorable locations in Humboldt and possibly Menclocino, Trinity and Siskiyou counties in California. The initiation of quantitative studies designed to follow the pattern of vegetational changes and the correlated beetle populations was reported by Iluff aker and Holloway (1949). A brief review of an important survey of these counties by Davy (1902) indicates: 1) The climax grass cover in this area probably consisted of Danithonia californica as the most important component. Other bunchgrasses such as Stipa, Melica, Elymus, Poa, and Festuca were represented, as were important associated forage species such as Trifoliuml spp. (annual and perennial clovers), Lath yrus spp. (wild pea vines), and Wyethia sp. (wild sunflower). 2) There were important early changes, apparently beginning with invasion of the region by such introduced annuals as Erodiumt cicutarpum (filaree) and Avenia fatua (wild oats), later followed, as a result of still heavier stocking, by Hordewun gussoneanum (foxtail), Festuca myuros (rat-tail fescue), and Browrus hlordeaceus (soft chess), and still later by the appearance of weedy arrivals during the last years of the past century. such as Erodium moschatum (musky filaree), Brownus rigidus (broncho grass) Hordeum murinumn (foxtail), Centaurea melitensis (tacaloti), Hypochoeris glabra (hawkbit), and Medicago hispida (burclover). The latter species and the filaree are considered of definite forage value. Some comparison of Davy's survey with the present quantitative results may be worthwhile. For example, Hypochoeris glabra was at that time making its appearance, but now is a definite pest. Also, E. cicutarium, the filaree which thrived prior to his study, is definitely not the species of Erodiurn now most common in either that area or at the 1 Presented in general terms, with slides, at the Western Section Meeting of the Ecological Society at Salt Lake City, June 22, 1950. The general project is under the coordinating supervision of J. K. Holloway and is a cooperative one under the direction of Professor H. S. Smith of the Division of Biological Control, University of California and C. P. Clausen of the Bureau of Entomology and Plant Quarantine of the U. S. Department of Agriculture. The author wishes to express appreciation for the cooperation and assistance given this work by the Division of Agronomy of the University of California, and to acknowledge particularly the help of Professor Ben A. Madson and A. H. Murphy. The detailed program of importation of the beetles, their distribution to the Klamath-weedinfested areas and the general progress of control of the weed, as distinct from this study of the associated vegetational changes in the specific study areas, is reported by Holloway and Huffaker (1951).