Vascular Plants of North Carolina
Account for Eastern Sampson's-snakeroot - Orbexilum psoralioides   (Walter) Vincent
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Author(Walter) Vincent
DistributionThroughout the eastern half of the Piedmont and most of the Coastal Plain, but seemingly absent in the northeastern corner of the Coastal Plain. Absent from the Mountains and western Piedmont.

In the strict sense, this species is now limited to the Atlantic Coastal Plain and into the eastern and central Piedmont. It ranges north to central VA, and south to northern FL; thus it is present only in five states -- VA, NC, SC, GA, and FL. The large range shown on the BONAP map is primarily now for O. pedunculatum, which has recently been split off from O. psoralioides.
AbundanceDespite the species occurring in most counties from the central Piedmont to most of the Coastal Plain (at least 54 counties), it is not a common plant in most areas. It is generally infrequent overall in NC, but can be locally fairly common in some Coastal Plain sites that are well-managed with fire. Despite it not being as common as it would appear from the county range map, the editors do feel that the NCNHP's State Rank of S3 is much too conservative, and it is suggested that S4 or S5 is more accurate. However, it is likely that the species has declined over the past few decades.
HabitatThis is a species of a wide array of mesic and moist habitats, yet it seems to have some particular habitat requirements that are not fully understood. For example, it occurs in glades, open pinewoods, powerline clearings, old fields, and woodland borders. However, it prefers a slight bit of moisture in its habitats, and can thus be found in savannas, loamy pine flatwoods, and sandhill seepages, and in the Piedmont more often in somewhat damp spots in powerline clearings. In the Coastal Plain, it is clearly favored by prescribed burning.
PhenologyBlooms from May to July, and fruits from July to September.
IdentificationThis is a species that usually grows in dense, mono-culture stands, making it much easier to spot by an observer than if it grew singly. It has an erect or slightly leaning stem up to about 1.5 feet tall, mostly unbranched or with one or two strongly ascending to erect branches. There are rather few leaves, each consisting of 3 leaflets, with each one of them being narrowly elliptic and about 2 inches long but just 2/5-inch wide. The petioles are somewhat long, at close to 1 inch long. The species is conspicuous when in bloom, as the flowering stalks are often 5-6 inches tall, with the last 2 inches being covered in a very dense spike or tight raceme of violet-blue to lavender-blue flowers. The recently split off O. pedunculatum is quite similar, as would be expected; it differs in many subtle characters, in that its calyx tube, fruits, inflorescence bracts, and leaflet undersides do not have glands (not sticky to the touch), whereas the Piedmont/Coastal Plain species is glandular on these parts. You may need a hand lens to check these, but normally a glandular surface will feel sticky when squeezed. The ranges of these two are not known to overlap in NC, with O. pedunculatum known only from the southern mountains, so far. As mentioned in Habitat, this species has a wide array of habitats, and thus it is very difficult to target places to look for it, particularly in the Piedmont. But, once seen, in its usually dense stands, it is a very showy species when in bloom.
Taxonomic CommentsRAB (1968) and some other references treated this taxon as a variety: Psoralea psoralioides var. psoralioides. This older name is a synonym of Orbexilum psoralioides var. psoralioides. Weakley and some other recent authors elevate it to full species status.

Other Common Name(s)The lumped O. psoralioides complex is traditionally named as Sampson's-snakeroot, an idiosyncratic name, but no other name has been much in use. With the splitting out of the two taxa, a modifier name is needed, and Eastern is in general usage.
State RankS3 [S4]
Global RankG5
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B.A. SorrieEcotone, E side Vass Road and S of June Johnson Road; 4 June 2016. HokePhoto_natural
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