Vascular Plants of North Carolina
Account for Small-leaved Meadow-rue - Thalictrum macrostylum   Small & Heller
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Section 6 » Order Ranunculales » Family Ranunculaceae
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AuthorSmall & Heller
DistributionVery widely scattered across the entire state, with records for at least 31 of them, practically from corner to corner. Yet, there are large holes in the range, and it appears to be very sporadic in the Piedmont; Guilford represents the only such county in the entire north-central part of the state. Thus, it is found mainly in the southern half of the mountains and the lower Coastal Plain.

This is a scarce species across its moderate range, with scattered records from central VA south to the FL Panhandle and AL. Despite many records from the NC mountains, it appears to be absent from TN.
AbundanceRare to locally uncommon in the southern mountains, and very rare in the northern half. Rare over the Coastal Plain as a whole, being locally uncommon in a few central and southern coastal counties. Very rare in the Piedmont. This is a Signficantly Rare species, as identified by the NCNHP. Though it gives a State Rank of S2, the fact that records are available from 31 counties, and NCNHP considers at least 22 counties to have current populations, the website editors feel that a rank of S3 is more appropriate, and possibly it could be moved to the Watch List. Note: The Digital Atlas of the Virginia Flora mentions that all VA specimens "need critical evaluation". This implies that specimens could be misidentified, and this also suggests that the NC records might include some specimens or observations that could use better evaluation.
HabitatThis species is hard to pigeonhole into a particular favored habitat. It typically occurs in damp to rich soil places, but many records are over high pH soil, and some of these are in somewhat dry glades and barrens. In general, it occurs in damp seepages, damp bottomlands or openings in swamps, marsh edges, and damp glades and barrens (or at least where there is some seepage). Owing to this disparity of consensus of habitats, it is very difficult to search for new populations of it.
PhenologyBlooms from May to June, rarely to August; fruits shortly after flowering.
IdentificationThis is a tall Thalictrum, often growing to 3 feet or slightly taller. The basal and stem leaves are mostly bi-ternately divided, but can also be more pinnately divided. The leaflets differ for most species in that they are often not 3-lobed, as some are simply elliptical or oblong without lobes. The leaflets are somewhat smaller than other tall species, being about 2/3-inch long and usually less wide. The leaflets are slightly revolute (rolled under margins), and are strongly reticulate-veined below. The large and open panicle of scattered flowers -- male and female on separate plants -- is similar to others; the filaments on the male flowers are not needle-like like on T. coriaceum, nor does it have the teeth on the leaflet lobes that this species has. Thus, it must be carefully separated from T. revolutum and T. pubescens, and the very poorly known T. hepaticum. T. revolutum has the leaflet undersides and peduncles with glandular hairs, and these should feel sticky to the touch, though a hand lens would be better to confirm this. T. pubescens has these parts glabrous as with T. macrostylum, but T. pubescens has these parts finely pubescent as opposed to glabrous in T. macrostylum. Another separating feature is that the leaflets in T. macrostylum can be entire or 3-lobed, and average only about 2/5-inch wide; others tend to have leaflets over 2/3-inch wide or more and most leaflets are 3-lobed. As a general rule, a tall Thalictrum growing in somewhat damp ground, especially if the soil is of high pH, and having often unlobed leaflets that are fairly narrow (under 1/2-inch wide), should be this scarce species.
Taxonomic CommentsNone

Other Common Name(s)Small-flowered Meadow-rue, Littleleaf Meadow-rue, Piedmont Meadow-rue. Though Piedmont Meadow-rue seems to be somewhat more prevalent on websites and in references, this is a very poor name -- it is less numerous in this province as compared with the Blue Ridge and the Coastal Plain. About half mention the small leaf size in the name, and both Weakley (2018) and NatureServe use this character in the common name.
State RankS2 [S3]
Global RankG3G4
State StatusSR-T
US Status
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