Know Your Natives – Scarlet Rose Mallow

Scarlet rose mallow or swamp hibiscus (Hibiscus coccineus) of the Mallow or Cotton (Malvaceae) family is a tall herbaceous perennial with large, spectacular, scarlet (rarely white) flowers. The genus name is an old Greek name for “mallow”. The specific epithet is Latin for “scarlet”. The species occurs in scattered areas of the Coastal Plain from Texas to Virginia. In Arkansas it is a plant of conservation concern, occurring presumably naturally only in Lafayette County, but known escaped in several others. Natural habitat consists of sunny to lightly shaded areas of fresh-water swamps, marshes and drainages.

Scarlet rose mallow has a few to multiple erect, terete, smooth and glaucous stems 3 to 6 feet tall, occasionally taller.  Although they die back to the root-crown in winter, they are tough enough to persist among the new growth for several years. Larger plants may have slender, axillary branches which may be several feet long. Branches and petioles (leaf stalks) are also glabrous and glaucous. Stems, branches and petioles are a pastel light green, with reddish shading on the sunny side.

Typical leaves, 5 to 6 inches wide on 2 to 6 inch-long petioles, have a hemp-like, palmate blade composed of five wide-spread, linear-lanceolate, toothed lobes that unite at the petiole or higher in the leaf blade. Leaves are alternate, glabrous, light to medium green above and somewhat lighter beneath. Margins may be highlighted in thin lines of red.

Photo 1: Typical leaves have five linear-lanceolate lobes that attach to the petiole; however, as shown at upper center of photo, less dominant leaves may have three lobes. Sunny sides of stems, branches and petioles have a reddish shading.

Although flowering of scarlet rose mallow may extend for a month or more in mid to late summer, the solitary flowers remain in bloom for only one day each. The large flowers (diameters of 4 to 6 inches!) grow from the axils of the uppermost several to dozen leaves of the stems and branches. Flower buds have a glabrous calyx of five triangular sepals aligned margin-to-margin and united in their lower portion. Subtending the calyx, a raised ring bears 10 to 15 free-standing, ascending, glabrous, linear bracts, the so-called epicalyx, typical of many genera of Malvaceae. The yellowish green sepals may be 2 inches long, the medium green bracts from 1 to 1½ inches long. The persistent calyx and bracts are set on pedicels to 4 inches long.

Photo 2: Flower buds are axillary from uppermost leaves. Leaf margins have irregular serrations. Leaf margins and upper midveins tend to have a reddish line.
Photo 3: Sepals, subtended by linear bracts, loosely protect developing flower buds. Flowers open and close during the daylight hours of a single day.

Large, showy corollas are comprised of five well-separated, spreading, ovate petals, narrowed at the base and flaring to a broadly rounded tip. Petals, inside and out, are red with the throat being deep vibrant red.

Photo 4: Single flowers grow from axils of upper leaves. Position of petals is off-set (alternate) from position of sepals. Linear bracts cradle the calyx. Photo – August 4.

Stamens are fused into a central tubular column (another distinctive character of the Mallow family) to 2½ inches long, through which emerge the 5 styles of the pistil. The styles terminate in disk-shaped stigmas. Along the upper third of the stamen column, slender-stalked anthers emerge. The round purplish anthers split and recurve to expose white pollen. Flowers do not have nectaries. After pollen has been disbursed, stigmas shift from being erect and clustered to recurved.

Photo 5: A central column consists of five styles that are enclosed in a staminal tube bearing stalked anthers. At this point during anthesis, the disk-shaped stigmas are still erect and projecting outward.

Photo 6: At the time of this mid-afternoon photo, petals are beginning to fade, pollen has been disbursed, and disk-shaped stigmas have recurved.

Following anthesis, corolla and stamen column quickly drop-off and the ovary is exposed. Fertilized ovaries, with five chambers, develop into large, glabrous, ovoid capsules. Viewed from the side, capsules have five rounded-triangular “panels” and a rounded apex.  Beginning at the apex, capsules split open into the chambers to release the numerous seeds. Dark brown reniform seeds, roughened by short hairs, are aligned in single rows on axile placentas. Seed dispersal is mainly by gravity and water movement.

Photo 7: Five-chambered ovaries develop into ovoid capsules. Sepals become almost leaf like and persist as capsules dry. The circular joint, at the upper portion of pedicel, can be seen below the capsule at left.
Photo 8: Dry hardened capsules split into the chambers. Dark brown seeds, attached to central placentas, have a roughened surface. An open space occurs at the center of the capsule between the five placentas. Photo – September 13.

Scarlet rose mallow may be appropriate for a garden or natural area with sunny wet areas, such as near ponds and boggy areas. It is a striking plant due to its size, distinctive leaves, and showy flowers. It is excellent as a specimen plant. With its height, stems may need staking. Plants may be lost due to dry soils and extreme cold. Plants, which readily reproduce by seed, can bloom in their second or third year.

Three other native, perennial, white- to pink-flowered species of the genus Hibiscus occur in Arkansas: halberd-leaf rose mallow (H. laevis), woolly rose mallow (H. lasiocarpos), and rose mallow (H. moscheutos). Additionally, two non-native species occur as escaped in the state: rose-of-Sharon (H. syriacus), a shrub, and flower-of-the-hour (H. trionum), an annual. Scarlet rose mallow is easily distinguished by its leaf shape and enormous scarlet flowers.

Article and photographs by ANPS member Sid Vogelpohl

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