Diagnostic Characteristics
Hemizonia pungens is an annual composite with rigid, bristly, freely branching stems reaching 10-120 cm in height. Following germination (in autumn - late spring depending on rains) the plants grow into small rosettes with distinctive pinattifid (twice divided) leaves. Rosettes bolt in late spring and early summer and plants may flower from late June through the summer depending on location and weather patterns. Large plants may have well over 100 flowerheads, while the smallest may have just one or two. It is one of the few species in its habitat that flowers so late in the season. Others include certain Hemizonia spp., Grindelia spp. and the non-native invasive yellow starthistle (Centaurea solstitialis).
The leaves and stems are rough to the touch with both long and short spreading hairs which may have tiny glands which exude a strong-scented resin. On bolted plants leaves are spine tipped and generally stiff; lower leaves are 5-15 cm long, linear-lanceolate and deeply pinnattifid; upper leaves are 1 to 2 cm long, linear to awl-like and spine tipped, glabrous to scabrous with stiff margins and generally with axillary leaf clusters.
The flowering heads are terminal on short lateral stems which are axillary along the main branches and have condensed internodes and crowded leaves. They measure 0.5-1.0 cm across and contain both disk and ray flowers. The leaves appear to be whorled or involucrate beneath some flowerheads, each of which has a single series of 25-40 true phyllaries. Each phyllary partly encloses a single pale yellow disk flower at its base. The ray flowers are 3-5 mm long and two lobed. They produce fertile seeds (achenes) which are about 2 mm long and beaked with a smooth or minutely roughened surface and without a pappus. The disk flowers are darker yellow but are usually staminate (male only) and do not produce fertile seeds. The receptacle is flat with chaffy, spine- tipped scales.
The Jepson Manual of Higher Plants of California (Hickman 1993) recognizes 4 subspecies of Hemizonia pungens: ssp. laevis; ssp. maritima; ssp. pungens; ssp. septentrionalis. These differ from one another in the shape of their receptacle bracts, roughness of leaves and bracts and size of flowerheads. Subspecies pungens was introduced to southwestern California and to Oregon and Washington (Hickman 1993)and is an agricultural pest in the Columbia Basin. Subspecies laevis is found in grasslands in the southern coast ranges and the Peninsular ranges of California and is regarded as rare.
An analysis of the flavonoids in exudates produced by the leaves of Hemizonia species indicated that the chemistry of all 18 species examined was distinct except H. australis and H. pungens ssp pungens(Tanowitz et al.). All 18 species contained patuletin, quercitin, 3-methylquercitin and luteolin). H. pungens also contained naringenin, 3-methylpatuletin and 5,3,4-trihydroxy-3,6,7- trimethoxyflavone.
A good illustration of the species may be found in Volume IV of Illustrated Flora of the Pacific States (Abrams and Ferris 1960). Another good, but small, illustration may be found in The Jepson Manual: Higher Plants of California (Hickman 1993).
Information for the description was taken from Abrams and Ferris (1960), Hickman (1993), Mason (1957) and Hitchcock et al. (1955).
Habitat
Hemizonia pungens grows in dry grasslands and seasonal wetlands and thrives on a wide variety of soils and will move into dryland cereal and irrigated crops. At the Cosumnes River Preserve, where it is native, it colonizes low areas that may be flooded following winter storms and is most conspicuous where the soil has been disturbed (by plowing, construction, etc.) and/or flooded for several weeks during the winter months. These areas support herbaceous vegetation dominated by introduced mediterranean grasses and forbs (Avena fatua, Hordeum leporinum, Bromus spp., Lolium multiflorum, Erodium cicutarium, and Centaurea solstitalis) and a few natives (Eremocarpus setigerus, Madia spp., Hemizonia spp., Amsinckia intermedia).
It is now difficult to determine the nature of the pre-settlement herbaceous vegetation but it is thought that native bunchgrasses, particularly Stipa pulchra, Elymus triticoides and Poa scabrella dominated with forbs such as Madia spp., Orthocarpus spp., Amsinckia intermedia, and Eschscholtzia californica occupying areas between bunches.
Spikeweed was introduced to northeastern Oregon and is regarded as a pest at TNC's Lindsay Prairie Preserve where it infests the big sagebrush bottomland community which has a heritage rank of G3-S2. Unfortunately, the community is in degraded condition. Erosion of the ephemeral creek bed that runs through the area and the consequent lowering of the water table are believed to have allowed several exotic species, including spikeweed, to invade. As a result, it is difficult to determine the area's original vegetation.
Heritage program ecologists believe the site was dominated by Big sagebrush (Artemisia tridentata) and Great Basin wildrye (Elymus cinereus). Saltgrass (Distichlis stricta), Sandberg's bluegrass (Poa sandbergii), and squirrel tail (Sitanion histrix) are also thought to have been present. Now, scattered, small patches containing only saltgrass are present and intervening areas have been taken over by spikeweed and other weedy species. Where patches of un-eroded soil remain, small clusters of natives like Sandberg's bluegrass, squirrel tail, and on rare occasions, Great Basin wildrye, hang on. The native shrubs Big sagebrush, grey rabbitbrush (Chrysothamnus nauseosus), and matchweed (Xenotriche sarathrae) have become more abundant than they are believed to have been originally but the only species in the community which occur with greater than 80% frequency (1 m2 frame) are Sandberg's bluegrass and the non-native weeds cheatgrass (Bromus tectorum) and spikeweed.
Soil grab samples from areas supporting conspicuous populations of the species on the Cosumnes River (CA) and Lindsay Prairie (OR) Preserves were analyzed for general fertility, salinity, sodicity and pH (Soil study 1995).
The portion of the Cosumnes River Preserve from which samples were taken may be inundated for several weeks at a time during rainy winters but was formerly farmed and supported a corn-wheat-tomato rotation. These soils were slightly acidic (pH 6.7-6.9) while those from Lindsay Prairie were nearly neutral to basic (6.9-10.0). Cosumnes soils were less sodic (0.1 - 0.85 meq/100g) and less saline (0.34- 0.8 mmhos/cm) than those from Lindsay Prairie (0.29-11.5 meq/100g and 0.4-2.4 mmhos/cm respectively).Cosumnes soils were richer in Phosphorus (13-37 ppm) Potassium (13-163 ppm) and magnesium (4.1-6.7 meq/100g) than Lindsay soils (6-18 and 6-18 ppm and 2.1-4.1 meq/100g respectively) but had lower levels of calcium (6.5-10.7 meq/100g at Cosumnes vs 4.7-34.6 at Lindsay).
Further analyses indicated that at Lindsay Prairie the distribution of Hemizonia pungens was correlated with the distribution of the more eroded, sodic soils (1994). This may be because these soils are too harsh for all but a few species, reducing the competition that keeps H. pungens out of other areas of the preserve. If this is true, the species may be limited to the Lindsay series and similar alkaline flood silt soils in this region.
Ecology
We found no literature on the ecology of Hemizonia pungens but some work has been done on other members of the genus. One study by Morse (1988) found that seed set in another summer-flowering species, H. luzulifolia DC ssp rudis, was insensitive to both atmospheric and soil drought. The plants coped with the drought by continual root growth into deep soil-water reserves and by storing water in extracellular polysaccharides. The polysaccharides apparently help maintain tissue water balance and buffer cells from rapid changes by releasing water as plant water status declines. Morse (1988) also found that tissue water storage (capacitance) of above-ground shoots increased from low values in the relatively wet spring to very high values in the hot, dry summer. Greenhouse studies indicated that the increase was genetically determined, not environmentally induced. During drought periods, plants that received moisture as dew were able to continue photosynthesizing longer and to keep their flowerheads open for pollinator visitation longer. The latter factor was important because Morse (1988) found that seed set could be limited by reductions in pollinator visitation resulting from early flowerhead closure. However, the primary factor responsible for limiting seed production was the destruction of flowerheads and seeds by herbivores.
We were not able to obtain information on the insects that feed on Hemizonia pungens. English-Leob (personal communication) made observations of the closely related species H. luzulaefolia in California's Central Valley and found that it was fed on by larvae of the noctuid moths Heliothodes diminutivus and Heliothis phloxiphaga, and the plume moth Trichoptilus californicus, a tree cricket (Gryllidae) in the genus Oencanthus, flea beetles (Chrysomelidae) and the spittle bugs Philaenus spumarius. Impacts: (THREATS POSED BY THIS SPECIES) Hemizonia pungens was introduced to the Columbia River basin of northeastern Oregon and southeastern Washington within the last century where it behaves as an invasive weed. In 1988 it was discovered on the 386 acre Lindsay Prairie Preserve in Oregon's Columbia River Basin. At that time it dominated a total of 4 acres but the infestation spread rapidly. By 1992, fifteen acres of the preserve were infested and spikeweed densities averaged 750 individuals m-2. Morrow County, where the preserve is located, has placed spikeweed on its Noxious Weed List as has neighboring Umatilla County and several counties across the river in Washington. In November 1992, Morrow county served the Oregon Field Office legal warning that it must control the infestation on Lindsay Prairie.
The species poses no known threats within its native range.