Diagnostic Characteristics
Distiguished from other southeastern Marshallia by leaves which are reduced in size upwards, 5-12 internodes above the first one and more than 0.4 inch long; and acute pointed bracts underneath the flower head (Strausbaugh and Core 1978, Pyne and Shea 1994).
Habitat
Along the flood-scoured banks of large, high-gradient rivers in the central Appalachians. The species is also reported from rocky lake shores, creek banks, bluffs and flood plains. It tends to occur in moist to wet sandy soil, in sandy/cobbley alluvium or in bedrock crevices along rivers. Deeply entrenched rivers of the Allegheny Plateau region support most of the populations. Marshallia usually grows in full sun, yet P.J. Harmon of WVHP, Paul Sommers of TNHP, and Charles Bier of PAHP report that the species occurs in various degrees of partial shade, but tends to flower most prolifically in open sunlight. Associated species in the West Virginia/Pennsylvania region include Rhododendron arborescens, Toxicodendron radicans, Rosa blanda, Platanus occidentalis, Salix spp., Trautvetteria caroliniensis, Liatris spicata, Houstonia caerulea, Houstonia serpyllifolia, Lyonia ligustrina, Physocarpus opulifolius, Aster linariifolius, Sanguisorba canadensis, Sorghastrum nutans, Andropogon gerardii, Zigadenus leimanthoides, Solidago spathulata ssp. randii var. racemosa, Platanthera clavellata, Oxypolis rigidior, and Allium cernuum. Along West Virginia's Gauley River, M. grandiflora occurs closely associated with plant species common to the tall grass prairie, such as Andropogon gerardii, Sorghastrum nutans, and Coreopsis tripteris. In Tennessee, Conradina verticellata is an associated plant species. Marshallia grandiflora is but one of several Eastern regional endemics and rarities known to be nearly or virtually restricted to flood-scoured riverbank habitats--others include Pedicularis furbishiae, Spiraea virginiana, and Astragalus robbinsii var. jesupi.