Vascular Plants of North Carolina
Account for American Senna - Senna hebecarpa   (Fernald) H.S. Irwin & Barneby
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Section 6 » Order Fabales » Family Fabaceae
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Author(Fernald) H.S. Irwin & Barneby
DistributionScattered over most of the mountains and Piedmont; does not occur in the Coastal Plain. There has been considerable confusion in the identification of this species and the very similar S. marilandica, though hopefully the specimen data are correct.

This is a Northern species, ranging from NH and southern WI, south to central NC and central AL.
AbundanceGenerally rare to uncommon in both regions, less numerous than the confusingly similar S. marilandica. This is a Watch List species, as assigned by the NCNHP.
HabitatThis is a species of moist to damp habitats, and it favors openings in bottomlands, creek banks, wet thickets, and edges of moist or rich forests -- typically in partial sun. Whether there is an affinity to circumneutral soils in the state is not certain, but it does not show a tendency toward "weediness" that S. marilandica often does.
PhenologyBlooms in July and August, and fruits from August to November.
IdentificationThis is one of two native species in the genus Senna that were formerly in the genus Cassia, with some other obviously different species. This is a fairly tall and robust species, growing erectly and to about 3' tall, rarely to 5' tall. Though essentially unbranched, it has very long leaves that make the plant appear branched and bushy. The leaves can be 10-12" long, and they are highly divided into 10-20 fairly large leaflets. Each leaflet is roughly elliptic and about 1.5" long and about 0.5" long, thus about 1/3rd as wide as long. (S. marilandica is essentially identical in these features.) In this species, there is a small somewhat club-shaped gland in the leaf axils, and this gland has a slightly narrow stalk (barely visible); in S. marilandica, these glands are rounded and essentially sessile. However, this is a very tricky field mark, in that the stalk is hard to see, and it is easy to call a Senna species as S. marilandica by this character when in reality it may be S. hebecarpa. The inflorescences of both species are also extremely similar; each has showy clusters of racemes in axils and at the summit of the stem. These flowers are quite large, bright golden-yellow and about 1" across. (There might be slight differences in the flowers or pattern of inflorescences, but these are not mentioned in various keys.) To be certain, you must have the pods present, and it is better to have some familiarity with one or the other species to feel comfortable. The pods of S. hebecarpa differ in three ways: 1) they are quite narrow, from 5-8 mm wide (about 1/4"), as opposed to 8-11 mm wide (about 2/5") in S. marilandica; 2) it is quite hairy overall (especially at first), as opposed to mostly glabrous in S. marilandica; and 3) the many segments of the pod are square-shaped (about as long as broad), as opposed to rather narrow (wider than broad) in S. marilandica. It should be mentioned that the shape of the pod segments can be tricky to judge without familiarity with both species, and the hairiness of the pods of S. hebecarpa can depend on fresh or old pods. Also, pods that are rather immature are obviously going to be smaller than when mature, and thus a developing pod of S. marilandica, when measured, may well be less than 8 mm wide. Thankfully, neither species is truly rare in the state, and ranges are somewhat similar, and thus mistaken identity when in the field is not overly critical, other than collecting one for an herbarium and getting the incorrect identification. However, it is quite important in establishing new county records for each. Field biologists often run across a few of these two species annually in their work, such as along greenways while walking in bottomlands, or along wet thicket margins; when in bloom, they are absolutely impossible to overlook. But, you almost certainly should re-visit the site(s) later in summer or fall, and identify the plants by the pods and not by flowers or glands.
Taxonomic CommentsBoth of these two species -- hebecarpa and marilandica -- were originally included uncomfortably in the large genus Cassia (as in RAB 1968), but all references today have then moved into Senna.

Other Common Name(s)Wild Senna, Northern Wild Senna. The name of "Wild Senna" is so generic that it could refer to either species, even if the latter is normally named as Maryland Senna.
State RankS2S3
Global RankG5
State StatusW7 [W1]
US Status
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