Know Your Natives – Patridgeberry

Partridgeberry (Mitchella repens) of the Madder (Rubiaceae) family is an evergreen perennial with a trailing growth habit. It occurs in the U.S. from Texas to Oklahoma to Missouri to Minnesota thence to the Atlantic and Gulf Coasts. It occurs throughout most of Arkansas except for portions of the Mississippi Alluvial Plain and calcareous areas of the Ozarks. Mitchella repens is one of only two species of the genus that have been identified worldwide*. The genus name honors John Mitchell, an 18th century Virginia native, who worked with Carl Linnaeus regarding the flora of the New World. The specific epithet is Latin for “creeping”. Other common names include twinberry and twin-flower. Its preferred habitat is moist, well-drained, acidic and sandy, rocky or loamy soils in partially shaded woodlands where leaf litter is thin, including mossy areas.

Partridgeberry’s ground-hugging stems intertwine to form mats. Stems have short pubescence when young. Stems occasionally produce single lateral stems as well as pairs of stems at stem tips. New stem segments, mostly green to reddish or with purple coloration, grow straight in open areas. New seasonal growth, which may be up to 10 inches long, grows from apical buds in telescoping fashion, with stem diameter and leaf size decreasing toward the apex. Older stem segments lose their leaves and become brown as they become covered by subsequent plant growth and leaf litter. New segments bear root nubs on their lower side near leaf nodes and randomly between nodes, from which roots may grow upon contact with soil. Fibrous, descending branching roots can be 5 or more inches long. Leafless stem segments, becoming a permanent part of a plant, toughen and become slightly gnarly with age, but do not increase in size.

Patridgeberry - Mitchella repensPhoto 1: Roots may grow from near leaf nodes or elsewhere from the underside of stems.

Opposite, orbicular to cordate leaves, borne mostly along current year’s stem segments, have ¼-inch-long petioles. Lower ends of petioles are set at an acute angle toward the stem apex while the upper portion trends upward to allow leaf surface to face sunlight. Largest leaves, at the base of current season’s growth, are ¾ to 1 inch in length and width. Upper and lower leaf surfaces are glabrous, with the upper surface being a shiny dark green as compared to the dull light green lower surface. Leaves appear leathery with a lighter colored main vein on the upper surface and secondary veins that bend toward the leaf apex (arcuate). The leaf blade is mostly flat, but turns down to join the petiole. While plant height on open ground is less than ½ inch, within mats or growing among plant litter, plant height may be elevated several inches.

Patridgeberry - Mitchella repensPhoto 2: Current-year stem growth shown across upper-center of photo. Angle of petioles changes to orient leaves to sunlight. Note pale midribs of leaves.

Patridgeberry - Mitchella repensPhoto 3: With several years of growth, older stems become covered by newer stem growth and leaf litter. Largest leaves are at base of current season’s growth.

The inflorescence develops in early to mid-spring at stem apices and from leaf axils. Two funnel-shaped, half-inch-long upright flowers share a stubby light green calyx that is on a short pedicel. Each calyx-half has four central points that are reduced calyx lobes. In bud, corollas are glabrous on their exterior, narrow at their white bases, and inflated at their light lavender upper ends. With anthesis, four broad lobes with obtuse tips spread wide, exposing a white interior with dense, long white hairs. Four stamens are sited between the lobes, adnate (fused) to the corolla tube just below lobes. Elongate anthers are aligned with the floral tube. A single style is topped with four long, down-turned stigmas. Stamens and pistil are typically white, although filaments may be tinged with purple. The nectary is positioned above the inferior ovary.

Partridgeberry has dimorphic flowers–they appear in two forms or morphs. One morph has a long style with its stigmas well exserted  beyond the corolla and stamens that remain within the corolla tube (referred to as the “pin” morph). The second morph has a short style so that stigmas remain well within the corolla tube, while stamens are exserted well beyond the corolla (referred to as the “thrum” morph). An individual plant bears flowers that are either pin or thrum, but not both. This intriguing adaptation that increases the chance of outcrossing, rather than self-pollination, is called heterostyly.

Patridgeberry - Mitchella repensPhoto 4: In this early May photo, flower buds are shown at the top of photo and several flower pairs and calyx pairs are shown lower in photo.

Patridgeberry - Mitchella repensPhoto 5: In this mid-May photo, flower buds are seen along with an open corolla that shows the pin morph of dimorphisim. Note arcuate leaf venation and calyx bearing two corollas.

After corollas fall off, the upper portion of the inferior ovary has two adjoining, flattened scars that are remnants of the perianth (calyx + corollas). With successful pollination, the two fused ovaries beneath the scars enlarge to form a single fruit (a berry-like drupe). The mature and very distinctive fruit becomes bright red and bears toward the tip its two now-prominent perianth scars, like two craters, no longer adjoining but now well separated due to the fruit’s enlargement. Fruits, about 1/3 inch across, are often persistent into spring. The thin red exocarp (skin) surrounds a white, mealy interior with about four embedded stones. The fruit is edible, but rather tasteless.

Patridgeberry - Mitchella repensPhoto 6: In this early December photo, this partridgeberry was growing among moss and lichens near pine trees. Perianth scars remain evident along with calyx remnants, especially in the upper fruit. Inset shows fruit’s interior and stones.

For a shade garden with acidic soil, partridgeberry is an excellent plant which is especially noticeable and decorative in winter. Low-growing stems bear year-round, fresh-looking leaves accented with small white flowers in mid-spring and strikingly red fruit from fall into spring. This shallow-rooted plant can be ideal as a ground cover or as understory to shrubs.

*The second species in the genus is Mitchella undulata which occurs in eastern Asia.  Appearance of this Asian species is similar to Mitchella repens.

Article and photographs by ANPS member Sid Vogelpohl

 

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