How to tell the difference between Saltmarsh Fleabane and Camphorweed.
Three species of Pluchea occur in Maryland and are:
- Pluchea odorata ( Saltmarsh Fleabane, FACW )
- Pluchea camphorata ( Camphorweed, FACW )
- Pluchea foetida ( Stinking Fleabane, OBL )
The purple-pink flowers of Pluchea odorata, saltmarsh fleabane (annual) form small pubescent heads in a flattish cluster at the ends of stems and branches. The plant is 3 feet or more tall, its alternate, ovate to lance-shaped leaves are often toothed. When bruised, the leaves emit a strong odor (overtones of camphor). Being a true halophyte, saltmarsh fleabane requires wet soil mainly in salty or brackish habitats and is found in coastal areas of the Chesapeake Bay. Saltmarsh fleabane occurs throughout the Maryland western and eastern shore.
A similar species, Pluchea camphorata, camphorweed (annual or perennial), of fresh rather than saline habitats, has thinner, often more serrate leaves and a rounded cluster of flower heads, these often with granular resin globules but nearly hairless. In both species the leaves are borne on short petioles or taper to the base. Camphorweed blooms from August through October, and occurs in alluvial swamps, especially in seasonally flooded sloughs, floodplain oxbow ponds, wet clay flatwoods and clearings, ditches and impoundment shores. Camphorweed is Maryland endangered, highly state rare (S1).
The leaves of the Pluchea foetida, stinking fleabane (perennial) are broad-based, clasping the shorter stem, and the flowers are creamy white. Stinking fleabane is found in only a few southern coastal plain counties. Stinking fleabane flowers from late July through October, and occurs on interdune swales and ponds, maritime swamps, depression swamps and ponds, wet flatwoods, sea-level fens, boggy clearings and ditches. Stinking fleabane is an annual, flowers from August and into October, and occurs in tidal oligohaline to mesohaline (rarely freshwater) marshes, tidal swamps, high energy tidal shores, maritime swamps, brackish interdune swales and ponds, rarely in impoundments inland. According to Maryland Biodiversity, stinking fleabane only occurs in Somerset and Worcester County.
So here is my quandary. I have a jobsite where it is important to confirm the species of Pluchea that I have. I am intimately familiar with saltmarsh fleabane, as I see it with regularity when I am boating. I have numerous photos of that plant that I have taken from my boat along the shorelines of fresh and salt tidal wetlands. Another species of Pluchea, which is very similar to the saltmarsh fleabane is the camphorweed. I had to employ some serious botany to discriminate between the two species, as I felt uncomfortable that my aggregate was saltmarsh fleabane.
So how to tell the difference between Pluchea odorata (common) and P. camphorata (an RTE species) in the field? First, stinking fleabane is not in contention, as it has white flowers and clasping leaves to the stem, but saltmarsh fleabane and camphorweed look nearly identical, and the internet is replete with mis-identification.
The Maryland State endangered camphorweed typically has granular, sessile (attached, immobile) resin globules on the leaves, a phenomenon that I have seen on a species of blueberry. They also have a very fine covering (puberulent) of hairs on the leaves and stems, whereas the saltmarsh fleabane has a more obviously pubescent covering.
The bracts that hold the flower of the camphorweed are not as long, layered or pronounced as in the marsh fleabane (note the hand drawn taxonomy graphic below).
Using these two diagnostics, my plants in question are the common marsh fleabane, as I could not find or feel any grains of resin on the leaves, and the bracts perform as shown in the graphic diagnostics. Otherwise, the plants that I observed in the field today are a touch atypical of others that I have seen in more favorable tidal shoreline habitat, and hence the higher level of scrutiny.
Flora of Virginia, 2012, Weakley, Ludwig & Townsend
Wildflowers and Grasses of Virginia’s Coastal Plain, 2013, Hamilton & Hall
Plants of the Chesapeake Bay, 2014, Musselman & Knepper
The Illustrated Companion to Gleason and Cronquist’s Manual, 1998, Holmgren, Jess, McCauley, Vogel