Virginia Sneezeweed

M. C. Simurda and J. S. Knox (2000) presented ITS sequence data that placed a population of Helenium virginicum from the Ozark highlands of southern Missouri in a monophyletic group with six populations of H. virginicum from the Shenandoah Valley of Virginia. R. L. Rimer and J. W. Summers (Missouri Department of Conservation, pers. comm.) located 42 H. virginicum populations in six counties in the Ozark highlands of Missouri. G. A. Yatskievych (Missouri Botanical Garden, pers. comm. to editors) has stated, ".. . the existence of this taxon in Missouri is no longer a matter of a single odd population, but probably rather another case of a taxon with two disjunct centers following dissection of a range during the Pleistocene glaciation."

Helenium virginicum is in the Center for Plant Conservation’s National Collection of Endangered Plants.

Perennials, 30–130 cm. Stems 1(–2), branched distally, strongly winged, glabrous or sparsely to moderately hairy proximally, glabrous or sparsely hairy distally. Leaves glabrous or sparsely to densely hairy; basal blades oblanceolate, weakly to strongly lobed; proximal and mid blades oblanceolate to lanceolate, usually entire, sometimes dentate; distal blades usually lanceolate, entire. Heads 2–25+ per plant, in paniculiform arrays. Peduncles 2–8 cm, sparsely to moderately hairy. Involucres globoid, 8–15 × 10–16 mm. Phyllaries (connate proximally) sparsely to moderately hairy. Ray florets 8–13, pistillate, fertile; corollas yellow, 10–15 × 4–10 mm. Disc florets 200–400+; corollas yellow proximally, yellow to yellow-brown distally, 2.5–3.5 mm, lobes 5. Cypselae 1.8–2.3 mm, moderately hairy; pappi of 5–6 entire, aristate scales 1.3–2 mm.

For about 50 years after Blake described H. virginicum in 1936, its distinctness from H. autumnale was doubted, and it was not treated as a good species by leading systematists such as Arthur Cronquist. Opinion changed when common garden comparisons, reciprocal transplant studies, and DNA sequence comparisons revealed that the two are distinct in morphology, ecology, development, and ITS sequence (Knox, Castanea 1987; Knox et al., Syst. Bot. 1995; Simurda et al., Syst. Bot. 2005). Key character differences between the two species are that the basal stem and leaves of H. virginicum that form above water are conspicuously pilose, where H. autumnale is glabrous, H. virginicum has lance-linear, mostly entire mid-stem leaves that scarcely taper toward the base and scarcely show secondary veins, while H. autumnale has leaves that are more frequently toothed, that taper more toward the leaf bases, and that show conspicuous secondary leaf veins. Basal cauline and rosette leaves of H. virginicum are sometimes deeply lobed, while those of H. autumnale are not. Achenes of H. virginicum are longer (mean 1.6 mm), and wider (mean 0.83 mm) than those of H. autumnale (mean length 1.3 mm, width 0.6 mm), and at maturity most corollas of H. virginicum abscise as they turn brown, while nearly all corollas of H. autumnale are retained on the achenes, though brown. Virginia populations of H. virginicum grow in sinkhole ponds that are lined with acid gray clay overlying 100 m or more deep acid alluvium that is perched on bedrock of limestone or dolomite. Erosion of the bedrock causes subsidence of the basin at the soil surface, permitting it to capture water, which may stand continuously for many months at wet times, but the basins do go completely dry either seasonally or supra-annually. Missouri populations of H. virginicum are much less well studied than Virginia populations, but a recent study (Rimer and Summers, Southeastern Nat. 2006) suggests that the habitat there is similar to that in Virginia in presenting a basin with acid soil overlying dolomite or limestone. Ecological studies of Virginia populations indicate that H. virginicum grows year round, forming linear basal leaves below water, and elliptic to obovate entire or lobed leaves above water; the plants are self-incompatible; seeds do not germinate in the dark or below water but may remain viable in the seedbank for more than a decade; plants do not survive to reproduce in the shade (Knox, J. Torrey Bot. Soc. 1997; Messmore and Knox, J. Torrey Bot. Soc. 1997; Adams et al., Biol. Conserv. 2005). Helenium flexuosum has a similar vegetative morphology to H. virginicum, though the plants of H. flexuosum seem to be shorter and there is no record of them growing in sites that flood for long periods. H. flexuosum has neuter ray flowers, in contrast to the pistillate ray flowers of H. autumnale and H. virginicum. Disc flowers of H. flexuosum are purple distally or throughout, while those of H. autumnale and H. virginicum are yellow proximally and yellow to yellow-brown distally (Flora of N.A., 2006).

Helenium virginicum is a rare species of flowering plant in the aster family known by the common name Virginia sneezeweed. It occurs in the United States, where it has a disjunct distribution; it is known only from Virginia and Missouri. It is limited to a specific type of habitat and it is threatened by modification of this habitat. It was federally listed as a threatened species of the United States in 1998.

At the time the plant received federal protection it was known from 28 populations in two Virginia counties. Soon after, a population of similar plants was found in Missouri and by genetic analysis were confirmed to be of the same species. Searches turned up a total of 44 occurrences in six counties in the Ozark Highlands of Missouri. This disjunct distribution was probably caused by the cleaving of the species' geographical range during Pleistocene glaciation, leaving two relict ranges.

Helenium virginicumis similar to and often mistaken for Helenium autumnale, the common sneezeweed. It is a perennial herb generally growing to a maximum height between 70 centimeters and 1.1 meters (28-44 inches), but it is known to reach 1.7 meters (68 inches or 5 2/3 feet) at times. There is a basal rosette of leaves and an erect, winged stem lined with lance-shaped leaves that become smaller toward the top of the stem. The inflorescence has several flower heads, each with a spherical disc covered with disc florets and lined with yellow ray florets just over a centimeter (0.4 inches) long. Blooming occurs in July through October. The plant is self-incompatible.

Helenium virginicum only grows near sinkhole ponds in the Ozark Highlands of Missouri and the western margin of the Blue Ridge Mountains in Virginia. These ponds are lined with clay or bedrock and are filled with water from about January to June or July each year. They may take the form of actual holes or they may be more like very wet meadows. The ponds are often actively grazed by cattle and can tolerate disturbance. The hydrology of the sinkholes varies seasonally and year to year, causing a similar fluctuation in the population and recruitment of the sneezeweed.

The greatest threat to this species is habitat modification. Destruction of the sinkhole habitat could lead to the extinction of the species.