American chaffseed, Schwalbea americana L., is a federally endangered hemiparasitic herb that requires a high fire-return interval, or fire surrogate to persist across the landscape. Due to extirpation of the species from 10 states, or more than half of its range, and a decline in known occurrences, American chaffseed was listed as an endangered species on September 29, 1992. Historically, this species occurred along the coast from Massachusetts to Louisiana and inland states Kentucky and Tennessee. Currently, this species occurs in seven states along the coast: New Jersey, North Carolina, South Carolina, Georgia, Alabama, Florida and Louisiana. American chaffseed has continued to decline since it was listed due to the persistent threat of fire suppression that results in vegetative succession or woody encroachment.
American chaffseed occurs in fire-maintained longleaf pine flatwoods and savannas. Often it is found in ecotonal areas between peaty wetlands and xeric sandy soils. Kral described American chaffseed habitat in 1983 as an open grass-sedge system in moist acidic sandy loams or sandy peat loams. Chaffseed is dependent on factors like fire, mowing, or fluctuating water tables to maintain the open to partly-open conditions that it requires. Historically, the species probably existed on savannas and pinelands throughout the coastal plain and on sandstone knobs and plains inland where frequent, naturally occurring fires maintained these sub-climax communities. Under these conditions, herbaceous plants like American chaffseed were favored over trees and shrubs.
Most of the surviving populations, and all of the most vigorous populations, are in areas that are still subject to frequent fire. These fire-maintained habitats include plantations where prescribed fire is part of a management regime for quail and other game species, army base impact zones that burn regularly because of artillery shelling and forest management areas that are burned to maintain habitat for wildlife like the endangered red-cockaded woodpecker. This species also find suitable habitats on various private lands that are burned to maintain open fields. Fire may be important to the species in ways that are not yet understood, such as for germination of seed or in the formation of the connection to the host plant.
A dense growth of trees and underbrush covering a large tract.
Areas such as marshes or swamps that are covered often intermittently with shallow water or have soil saturated with moisture.
American chaffseed is an erect perennial herb with stems that branch only at the base. The leaves are alternate, estipulate, sessile and ascend in an overlapping spiral, as Kral documented in 1983. The leaves, stems and flowers are villous-puberulent, meaning hairy throughout. The five-lobed flowers are reddish-purple and mature into dehiscent capsules that contain numerous linear, yellowish-tan seeds. The showy flowers have a high degree of bilateral symmetry, elaborated for pollination by bees, as documented by Pennell in 1935. Flowering occurs from April to June in the southern part of its range, and from June to mid-July in the northern part of its range. Fruits start to mature in early summer in the south and October in the north, as was documented by Johnson in 1988
In the field, germination and seedling recruitment appear dependent upon microsite soil disturbances such as earthworm castings, pocket gopher activity, as documented by Kirkman and Drew in 1995, as well as old fire plow lines and old logging roads, as observed by April Punsalan in 2016. Other minor disturbances, like prescribed fire, that expose bare soil aid in germination and seedling recruitment. American chaffseed does not reproduce asexually via vegetative storage organs, like rhizomes, bulbs, corms, therefore recruitment is solely dependent upon sexual reproduction.
In controlled conditions, germination is high, with roughly 90% of all seeds sown immediately after collection, or within 24 hours, and one to two years after collection, as noted by Kirkman in 1993 and confirmed by Van Clef in 2001. Due to American chaffseed’s hemiparasitic nature, seedlings have to be given additional nutrients or grown with host species, like narrowleaf silkgrass, to survive off-site conservation safeguarding efforts. In 2002, Norden demonstrated that low soil moisture or low water availability may inhibit seed germination and seedling establishment. Because American chaffseed does not reproduce asexually and seeds do not survive long in the soil seedbank, soil disturbance via prescribed fire or other disturbances that expose bare soil which is critical to the recruitment and survival of this species.
In 2002, Norden illustrated that buried American chaffseed seed will persist in the soil and remain viable for at least one year. In 2003, Kelly demonstrated that no germination occurred for seeds stored in field conditions for five years. Thus, American chaffseed does not appear capable of long-term dormancy within the soil, as noted by Kelly in 2003 and later by U.S. Fish and Wildlife Service biologists in 2008.
The morphology of American chaffseed seed, somewhat flattened and compressed and enclosed in a loose-fitting sac-like, suggests wind dispersal. However, no information is available to support this hypothesis. Information is lacking on both the mechanism and distance of seed dispersal. Initial observations in New Jersey determined that ants ignored American chaffseed seeds in 1995, as documented by T. Hampton, with the New Jersey Office for Natural Lands Management. Therefore, ants unlikely serve as dispersal agents.
American chaffseed is a monotypic genus, meaning that only one species occurs in the genus Schwalbea-Schwalbea americana.
American chaffseed is a hemiparasitic herb that photosynthesizes in addition to acquiring photosynthates via modified roots, haustoria, which connect to the vascular system of host species. Although American chaffseed can form haustorial connections, through a highly-modified stem or root, with a wide variety of species, narrowleaf silkgrass (Pityopsis graminifolia) appears to be a favorable host species along with other composites and grasses, as was noted by J. Glitzenstein and others. This relationship may be, in part, due to composites and grasses having a higher density of roots near the soil surface thereby increasing the likelihood that American chaffseed seedlings come into contact with the roots of host species, as was noted by U.S. Fish and Wildlife Service biologists in 2008. American chaffseed is considered the rarest root parasitic plant in the south. However, because there are many common hemiparasitic species, American chaffseed’s hemiparasitic nature does not necessarily contribute to its’ rarity, as documented by Obee and Cartica in 1997.
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