Salt Marsh Fleabane

Pluchea odorata

purple flowers bunched together on top of stems
Santa Helena trailhead | September 2017

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.

Other Common Names:

sweetscent, shrubby camphor weed, sourbush, purple pulchea, stinkweed

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.

small white hair-like seed under microscope

Seed with attached pappus (next to a dime) | August 2016

white hair like seed under microscope

Central, pistillate flower | August 2016

close up of single purple flower pod

Outer, staminate flower with sterile pistil | August 2016

Distribution 7,89,295

Salt marsh fleabane ranges naturally across the tropics of the Americas, across northern South America, through the West Indies and Mexico and across the southern portion of the United States. It has invaded the Great Lakes 295 and Hawaii, where it is considered a noxious weed,126  and it has been declared endangered in Pennsylvania.126

Salt marsh fleabane is a plant of moist regions that likes wet soils and is tolerant of elevated salinity. “It doesn’t like Nouveau Wet places, only Old Damp.” 293

Salt marsh fleabane can be quite abundant in the Reserve, especially in the alkali marsh east of the freeway, but its soft colors often cause it to blend into the surrounding vegetation, Given appropriate lighting, clusters of fleabane emerge as bright patches and stripes across the marsh. The precise location tends to move from year to year, probably in response to the water supply. In 2008 it was easily seen along the access road to Stonebridge Plateau. In 2016 it was not found there but occurred in large numbers between the dike and the freeway. A few plants occur sporadically in other damp areas, such as north of Stonebridge in the Escondido Creek drainage, along the Pole Road and the under the willows at the Nature Center.

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.

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

Alternate Scientific Names:

Pulchea carolinensis, Pluchea purpurescens, Conyza odorata

Jepson eFlora Taxon Page
close up of purple flower pods bunched together

Dike | August 2016

river with purple flowers on each side

Dike | August 2016

field with purple flowers throughout

Pole road | September 2009

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.

field with purple flowers

Dike | August 2016

purple flowers in field

Santa Helena trailhead | September 2009

tiny purple flower pods bunched together on branch

Like other late summer bloomers, salt-marsh fleabane support many pollinator and pollinator predators

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

field of purple flowers

Pole road | September 2009

branch with tiny purple flowers bunched together

Pole road | August 2016

green leaves

Nature Center | August 2016

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 arrowweed is not welcome in San Elijo Ecological Reserve.

As a part of our dune restoration project, desert arrowweed 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.

purple flowers bunched together on branch

Santa Helena trailhead | August 2009

women inspecting the plant and purple flowers

Denise Stillinger with desert arrow-weed | West Basin | July 2009

field of purple flowers

Dike | August 2016

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