The Napaea Page

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Introduction

Napaea is a monotypic genus of tall perennial Malvaceous herbs, endemic to central and eastern USA, occasionally grown as an ornamental plant. It is usually known in English as the Glade Mallow.

Classification

The genus was introduced by John Clayton in his Flora Virginica and taken up by Karl von Linne (Linnaeus) in his Species Plantarum. As the starting point for nomenclatural priority is the Species Plantarum, authorship is conventionally ascribed to Linnaeus.

The name is taken from the Greek ναπη, a wooded valley or mountain glade. This is said to be in reference to the locations in the species is found. However in much of the range of the species it occurs not in woodland or mountains, but in wet regions of prairie habitats. The name (and the vernacular name of Glade Mallow) may come from its original discovery in Augusta County in the mountainous parts of western Virginia.

A number of other species have been described within this genus, but they have all been reduced to synonymy with Napaea dioica (the type species) or with species in another genus. The species is related to other North American temperate mallows, such as Sidalcea, Modiola or Callirhoe, although in the past it has been considered related to species in Herissantia, Abutilon, Sida, Malachra, Asterotrichion, Gynatrix and Plagianthus. Published ITS DNA data sequences place it closest to Modiola and the related South American Modiolastrum. On morphological grounds I would place it close to Callirhoe, but the ITS data is equivocal on this point.

Napaea is also a genus of South and Central American butterflies, and is also a synonym of the Eurasian butterfly genus Boloria.

Napaea dioica L.
English (American) Glade Mallow
Estonian napa

Napaea dioica is a robust herbaceous perennial growing to approximately 2 feet across by 3 feet tall, surmounted by flowering stems reaching 4 to 8, or exceptionally 10 feet. The foliage is composed of large (up to 10" across), alternate (one per leaf node), leaves (described as being similar to those of Ligularia), which are deeply divided into 5 to 9 palmate lobes, each lobe being acuminate and pinnatifid or coarsely serrate. The leaf-stalks are flanked by large (2-3 cm long, 4-9 mm wide at the base) persistent stipules.

In common with most mallows, parts of the plant are hairy. This indumentum varies between stellate (forma stellata Fassett) and simple hairs, but the variation does not show a simple geographical distribution.

Napaea dioica is dioecious, i.e. has separate male and female flowers borne on different plants. In both cases the flowering stems bear large branched clusters of flowers: technically they are panicle-like with umbellate subunits. The flowers are fragrant. They are relatively small compared to most mallows. They are borne in mid-summer, the display lasting for about 1 month. They lack an epicalyx (a trait connecting the genus with some species of Callirhoe, which also deviates from the usual Malvaceous state of bearing hermaphrodite flowers). The persistent calyx is small (about ½" long), and rounded at the base; the upper half is divided into 5 lobes. In common with almost all other malvaceous plants it is valvate in bud; i.e. the edges of the lobes touch, but do not overlap. The petals are white, and about ½" long. They are obovate in shape with a distinct basal claw which is adnate (joined) to the base of the staminal column. In the staminate (male) flowers a narrow staminal column, dilated at the base, is surmounted at the top by a globular cluster of 15 to 20 single-celled, reniform, anthers borne on a single whorl of short filaments, and pistils are completely lacking. In the pistillate (female) flowers 6-9 (8-10 according to some sources) slender style-branches, with introrsely decurrent stigmas, emerge from a rudimentary staminal column, which is surmounted by short antherless filaments or lobes; the ovary is divided into as many uniovulate locules.

The fruits are oblate, glabrous, schizocarps, 5-7 mm in diameter, breaking up into 6-9 (8-10 according to some sources) single-seeded papery mericarps. These are shaped like the segments of an orange (similar to those of, e.g., Lavatera cretica), but usually with a small beak-like protrusion at the top. They are indehiscent, or tardily breaking in half to release the seed. The seeds are reniform, and 3 mm long.

The root system of Napaea dioica consists of a large hollow tap-root with occasional branches.

Pollinators include bees, hover flies and blow flies.

Distribution and Habitat

In the wild Napaea dioica is found in the northern parts of the central and eastern United States, from southeastern Minnesota and northeastern Iowa, through southern Wisconsin, northern Illinois and Indiana to southern Ohio, and disjunctly in Wythe County, Virginia and Windsor County, Vermont. It may also be present in parts of Pennsylvania. It is rare in Indiana and threatened in Iowa and Minnesota.

Contrary to the implications of both the botanical and vernacular names, in the west of its range Napaea dioica is a plant of moist areas in open habitats, rather than shaded clearings in woodland. It may be found in alluvial meadows and poorly drained areas of prairies, on lake shores, in ditches and marshy ground, in sun or semi-shade, and is most often seen in areas of moist, rank, weedy, vegetation.

Pests and Diseases: Reported as being susceptible to Malva vein clearing potyvirus; however it is not a natural host for this virus.

Cytology: The diploid chromosome number for Napaea dioica is 30.

Cultivation

Napaea dioica prefers a well-drained, humus-rich, soil, and full or partial sun. It is intolerant of drying out, the leaves rapidly wilting, and may be a suitable subject for a bog-garden. The tall flowering stems are vulnerable to wind damage, and the plant may benefit from a location which provides some shelter from wind.

Propagate from seed. Seeds should be covered, as darkness is needed for best germination. Germination should occur in a few weeks at 20°C. (It may be the case that the seed requires chilling before germination, i.e. cannot be sown fresh. Storing the seed overwinter in a fridge should meet the requirements for chilling.)

Images

  • photographs at Department of Botany, University of Wisconsin Madison
  • photographs at Illinois Natural History Survey
  • photograph of fruits at University of Indiana Urbana-Champaign
  • photograph of herbarium sheet of forma stellata Fassett at NYBG
  • Synonyms: Synonyms of Napaea dioica include  Napaea dioecia Hill, Napaea dioica f. stellata Fassett, Napaea laevis L., Napaea lobata Moench., Napaea palmata Moench., Napaea scabra L., Schizoica laevis Alef., Schizoica palmata Alef. and Sida dioica Cav.

    References

    1. International Plant Name Index
    2. USDA Plant Database
    3. Clemens Bayer, in Kubitzki & Bayer, The Families and Genera of Vascular Plants, Vol. 5 (2003)
    4. Hutchinson, The Genera of Flowering Plants
    5. Harold William Richett, The Wildflowers of the US
    6. Isaac Sprague and Asa Gray, The genera of the plants of the United States (1849)

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    © 2003, 2005 Stewart Robert Hinsley