Salt Marsh Fleabane

Salt marsh fleabane (Pluchea odorata) is a charming plant with soft, bright green leaves and tiny magenta flowers in large, rounded clusters. It is a plant of contradictions. In late summer it is often very abundant but is rarely noticed. It can stand out as bright purple stripes and patches and an hour late vanish, fading into the soft colors of the marsh. Salt marsh fleabane is pungent, but the odor is described differently by different people, a puzzle that has given rise to such disparate names as “sweetscent”, “sourbush”  and “stinkweed”.

Salt marsh fleabane is native to a tropical band across North and South America and the Caribbean. It is endangered in Pennsylvania), and, at the same time, an invasive noxious weed in Hawaii.

Description ^{2,4,34,59,292}

Salt marsh fleabane is an annual or short-lived perennial herb that produces one to several upright stems from a subsurface rhizome. Stems are generally less than four feet (1.5m) tall, green or purple/brown near the base. Stems and leaves are covered with short glandular hairs that give the plant a soft, velvet feeling and secrete a sticky, pungent substance. The odor has been called  “spicy,”^4,59 “camphor-like, “¹²⁶ “ill-scented” ²⁹⁴ and “downright weird.”²⁹²

The ovate leaves are soft green; the larger ones are about five inches (13 cm) long and about 2 3/4 inches (7 cm) wide. Leaf margins are smooth or with small, widely spaced teeth; margins sometimes have a pinkish tinge.

Small flower heads are arranged in flat-topped or round-topped terminal clusters.  The urn-shaped receptacle has about two dozen phyllaries in several series. Phyllaries are green below rapidly becoming magenta above. There are no ray florets. The outer disk florets are pale cylinders; each expands to three or four magenta lobes less than 1/64 inch (0.4 mm) across; these florets lack stamens and have one pistil with a slender magenta two-branched style and linear stigmas and a pale pappus. The ovary is inferior. The inner disk florets are somewhat larger than the outer florets, each pale cylindrical corolla expanding to five magenta lobes about 1/32  inch (0.7 mm) across. The inner florets are functionally male with a sterile pistil with an unbranched style surrounded by five stamens with the anthers fused into a tube around the style. Anthers are magenta with white pollen. Most flowers bloom between March and July.¹

The fruit is tiny (1 mm), dry and one seeded, attached to a bristly parachute (the pappus) at one end. The pappus is about 1/8 inch (1/2 cm) long, tawny at the base, becoming whiter at the ends.

Classification  

Salt marsh fleabane is a dicot angiosperm in the sunflower family (Asteraceae).² This is the largest family of vascular plants in the Northern Hemisphere.¹⁴³  “Flowers” of Asteraceae are made up of one or both of two types of flowers (florets): symmetrical disk florets and strapped-shaped ray florets. These are crowded onto a common base (receptacle), and together are often assumed to be a single flower, which we call a flower head.^{44 49,143}

Other familiar Asteraceae that occur in the Reserve include bush sunflower (Encelia californica), goldenbush (Isocoma menziesii), and coyote brush (Baccharis pilularis).⁴⁸

Species in the genus Pluchea lack ray florets.  There is one other species of Pluchea in the Reserve, desert arrowweed, Pluchea sericea.⁴⁸ This is a desert species, not native to this area, and it has been largely, if not entirely, removed from San Elijo Lagoon Ecological Reserve.

Currently, in 2018, only one variety is recognized in California, var. odorata.

Ecology ^41,271

Salt marsh fleabane reproduces both sexually from seeds and vegetatively from rhizomes. Rhizomes are underground stems that produce new plants genetically identical to the parent. Rhizomes may also store carbohydrates, proteins, and nutrients. Thus rhizomes allow the plant to survive during unfavorable conditions, and they fuel rapid growth when conditions improve. Rhizomes may also help anchor the plant to the substrate.

Many plants have rhizomes, including iris, asparagus, and quaking aspens, but marshy environments have a higher than normal proportion of rhizomatous plants. Rhizomes may be particularly advantageous in wet environments where both water level and water motion can be unpredictable.

Human Uses  

We have not located any uses of salt marsh fleabane by local Native Americans, but the plant appears in modern herbal remedies as a treatment for stomach cramps, from a variety of causes.^{292, 293}  A fresh infusion is an effective eyewash, and in the early 20th century, a concentrate was sold as a substitute for coffee.

Recently, a  pharmacological study, guided by the ancient and highly developed medicinal traditions of the Maya in Guatemala and Belize, studied the medicinal potential of compounds in salt marsh fleabane. Maya healers still use decoctions of this plant to treat coughs, colds, neuritis, and arthritis. The researchers found that extracts of salt marsh fleabane have strong anti-cancer effects and warrant  further studies.²⁹⁶

Interesting Facts  

Desert arrow-weed (Pluchea sericea) is closely related to salt marsh fleabane. Desert arrowweed is an upright, willow-like shrub  native to the riparian areas of desert canyons.  Although technically a California native species, it is not native in San Elijo but became established in West Basin many years ago where it flourished and overgrew precious sand dune habitat. Thus, unlike salt marsh fleabane, desert arrow-weed is not welcome in San Elijo Ecological Reserve.

As a part of our dune restoration project, desert arrow-weed was the target of a concentrated removal project lasting several years. Recently (summer 2016) newly dredged sand from the estuary entrance was deposited on previously overgrown land in order to sculpt new dune topography in the hopes of expanding our fragile beach dune habitat.