Know Your Natives – Camphorweed “Blooms” Frost Flowers

Camphorweed (Pluchea camphorata) of the Asteraceae (Aster) Family occurs in the Southeast and lower Midwest from Texas and Kansas to Illinois, Ohio, New Jersey and southward.  In Arkansas, the species occurs statewide, though is somewhat less frequent in the central Ozarks.  Camphorweed, an annual to short-lived perennial herb, grows at the edges of ponds and lakes, in marshes, on creek and river banks, in bottomland forests and in other moist areas.  In its preferred habitats, this species can become weedy.

Camphorweed, a.k.a. stinkweed, marsh fleabane or Plowman’s-wort, is an erect plant growing three or more feet tall.  Plants, with one to several erect, round, hairy and semi-woody stems, have an almost overpowering, musky (camphor-like) aroma when handled.

Alternate, ovate to broadly elliptical simple leaves are largest mid-stem of main stems.  There is one leaf per node.  Leaves, on short petioles, are acutely tapered toward the tip and broadly tapered toward the base.  The leaves, which are sticky (due to glandular hairs), have shallowly serrate margins with widely spaced teeth.  The veins are pinnate and raised on the lower leaf surface.  The upper leaf surface is covered with sparse, soft hairs while the lower surface is more densely hairy.

Sweetscent in spring showing beginning of inflorescence.

Spring growth of Camphorweed with beginning of inflorescence at top of the stem.

Inflorescences in mid-summer consists of rounded clusters (panicles) of cream-colored to pinkish-rose-colored terminal flower heads at the top of small plants or at the ends of many branches and sub-branches on larger plants.  Each flower head has the outer flowers  pistillate, with a highly reduced corolla, and a smaller number of staminate central flowers.  As in all members of the Aster Family, the ovary is inferior, with the corolla attached at its tip.  Corollas of the central flowers are round (radially symmetrical) with five lobes, and appear bisexual with one style and five stamens, but the style is undivided and the ovary sterile.

The involucre, which supports the head as a calyx would an individual flower in most other families, comprises overlapping bracts (phyllaries) that are ovate to linear in shape and similar in color to the flowers.  The appressed phyllaries tightly clasp the flower head.

Large and small plants of Camphorweed in bloom.

Photo 3

A panicle of Camphorweed flower heads.  Note the infertile pistils on central flowers.

One-seeded fruits, in mid-fall, are tiny achenes tipped with a bristly pappus. Like closely related sunflower “seeds,” (what we call seeds are actually fruits), the wall of the fruit (pericarp) is not fused to the seed inside.

Photo 4

Camphorweed in seed after a “killing frost.”
Fertile and infertile achenes set to disperse.

Photo 5

Frost flowers on Camphorweed.

Two other species of Pulchea are known from Arkansas: Pulchea odorata (sweetscent) and Pluchea foetida (stinking camphorweed).  Sweetscent differs from camphorweed in having inflorescence panicles strictly terminal or branching from only the upper nodes, elongated to nearly the level as the terminal panicle, giving the entire inflorescence a somewhat domed, flat-topped or layered appearance.  The flower heads of sweetscent are consistently deep rose-purple and the phyllaries are more densely hairy.  Sweetscent occurs in Arkansas primarily in the Coastal Plain and Arkansas River Valley, with a few scattered inland occurrences in the Ouachita Mountains along major rivers.  Stinking camphorweed differs from the previous two in having sessile, clasping leaves and flowers consistently light cream-colored.  It occurs in Arkansas exclusively in the Coastal Plain.  These two latter species can also produce frost flowers.

(For information regarding formation of frost flowers, see aKnow Your Natives” article posted November 26, 2013) link.

Article and Photos by ANPS member Sid Vogelpohl

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