Vascular Plants of North Carolina
Account for Slenderleaf False-Dragonhead - Physostegia leptophylla   Small
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Section 6 » Order Lamiales » Family Lamiaceae
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DistributionLimited to the lower Coastal Plain, in a narrow NNE-SSW band near the southern coast and northward near the upper end of Pamlico Sound and the northern side of Albemarle Sound. This is a species that was subsumed within Physostegia purpurea (formerly Dracocephalum purpureum) in many references. Some of the specimens of this species in SERNEC are still labelled as P. purpurea, based on range.

This is an Atlantic Coast species, ranging near the coast from southeastern VA south to central FL and and the FL Panhandle.
AbundanceRather rare to locally infrequent, but as some confusion exists between this species and P. purpurea, exact details of the range and abundance are not finalized. However, with records for at least 13 counties, and NCNHP not considering this as a Watch List species, it is not a rare species in general.
HabitatThis is a wetland species of near-tidal waters, but in fresh to slightly brackish situations. It is found in marshes, swamp openings, and wetter parts of bottomlands.
PhenologyBlooms from late May to early August, and fruits from June to September.
IdentificationThis is a rather tall and slender, wand-like herb that grows to 3-4' tall, often in dense stands. It has only a few opposite pairs of leaves scattered along the stem, with the larger ones (along the lower stem) having blades about 2-2.5" long, with a petiole about 1" long, elliptical to slightly lanceolate, with serrated margins. These larger leaves tend to be slightly wider just below the middle of the blade, whereas the very similar P. purpurea has similar lower leaves that are slightly wider above the middle (i.e., slightly oblanceolate). However, the upper two pairs of leaves are very different between these two; in P. leptophylla, these are smaller than the lower, but still about 1" long, much longer than the bracts in the inflorescence above. In P. purpurea, the upper pair of "leaves" are practically scales, no larger than the floral bracts, and the second highest pair is also quite small. Thus, the stem of P. purpurea generally looks quite "naked" for 1-foot or more below the lowest flowers and the lower leaves, whereas P. leptophylla has leaves that gradually become smaller toward the inflorescence. Also, the leaves of P. leptophylla are thin and flexible, often horizontally arranged, whereas leaves of P. purpurea are thick and fleshy, with the lower ones being ascending. The inflorescences of these two are quite similar, basically being a tall raceme at the end of the stem, reaching about 6" long or more, with the rose-pink flowers being fairly crowded; each flower is arranged horizontally, tubular with a swelling in the middle of the tube, and about 1.5" long. The habitats of these two are quite different; P. leptophylla grows in more marshy and swampy habitats, in richer soils, whereas P. purpurea grows in more acidic soils of wet pine savannas, ditches close to such pine stands, and other similar places. As mentioned above, this species can grow in very dense stands, and thus when in bloom it can be quite spectacular.
Taxonomic CommentsConsidering the many distinct differences between this species and P. purpurea, how and why it was often lumped in the past (or at the present time) is hard to fathom. Note that older references placed these species in the genus Dracocephalum, as in RAB (1968).

Other Common Name(s)Swamp Obedient-plant, Tidal Marsh Obedient-plant
State RankS2S3
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