Swamp rose-mallow (Hibiscus moscheutos) COSEWIC assessment and status report: chapter 3

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Species Information

Name and classification

Hibiscus moscheutos is a taxonomically difficult species and in the past has been divided into two separate taxa, with northern plants referred to as H. palustris L. or H. moscheutos ssp. palustris (L.) R.T. Clausen and southern plants as H. moscheutos L. or H. m. ssp. moscheutos (L.) R.T. Clausen (Fernald, 1942; Clausen, 1949).

The primary characters used to separate these taxa are petal color and leaf shape. Hibiscus palustris L. is distinguished by its pink flowers and three-lobed leaves, while H. moscheutos L. is characterized by white flowers, with red centres, and lanceolate leaves. While these extreme morphologies are distinctive, populations are often found with various combinations of white and pink flowers with or without red centres and various leaf shapes. This integration is particularly pronounced in a zone extending from New Jersey to Virginia, where the ranges of the two taxa overlap (Blanchard, 1976). However, even at the edge of the range, such as in Ontario, populations can be found with variable leaf shapes and flower color. It is therefore best to recognize all these plants as H. moscheutos L. without further dividing this species taxonomically (Blanchard, 1976). Blanchard (1976) has also treated the midwestern species, H. lasiocarpus Cav., as a subspecies of H. moscheutos L.

Description

Hibiscus moscheutos is a robust perennial growing to two metres in height with up to eight showy blooms found in the axils of the upper leaves. The large hollyhock-like flowers are unmistakable, with the pink or white petals 6-10 cm long. The flowers are hermaphroditic, and as is characteristic of all mallows, the stamens are united into a column arising from the centre of the flower. The style protrudes from the tip of the staminal column and is tipped with five round stigmas. When not in flower, the combination of tall stature, pubescent oblong or maple-like leaves, and subglobose capsules is distinctive (see Figure 1).

It should be noted that a collection of H. laevis was made from Pelee Island in 1904 by H.H. York (Stuckey, 1968). This was the first and only collection of this species from Canada (Oldham, 1983). Hibiscus laevis is similar to H. moscheutos but differs in having essentially glabrous, hastiform leaves. Recent authors (Stuckey 1968; Oldham 1983) have suggested that H. laevis is expanding its range northward and should be looked for in southwestern Ontario.

Figure 1. Hibiscus moscheutos flower (photo, Bruce Ford)