1. Rhododendron prinophyllum (Small) Millais (roseshell azalea, mountain azalea, wild
honeysuckle, election pink)
Azalea
prinophylla Small
R. roseum (Loisel.) Rehder
R. roseum f. albidum Steyerm.
R. canescens Porter (1889), not (Michx.) Sweet (1830)
Pl. 375 h–j; Map
1644
Plants shrubs or
small trees, not colonial. Stems 0.8–3.0 m tall, the bark dark gray, often
becoming scaly with small plates. Twigs densely and often minutely hairy,
reddish brown, becoming brown to dark gray, the winter buds ovoid, with several
overlapping scales, these sparsely and minutely hairy on the outer surface.
Leaves tending to be clustered near the branch tips, short-petiolate. Leaf blades
4–9 cm long, 2–4 cm wide, ovate to obovate, the margins entire and short-hairy,
sparsely hairy on both surfaces, the main veins of the undersurface densely
hairy. Inflorescences short, umbellate racemes of 4–13 flowers, appearing
before or with the leaves. Flowers slightly zygomorphic, hypogynous, fragrant.
Calyces deeply 5-lobed, 1.0–1.5 mm long, the lobes rounded to bluntly pointed
at the tip, densely glandular-hairy. Corollas trumpet-shaped, the tube 1.2–1.8
cm long, flaring to spreading lobes 1.1–1.6 cm long, rosy pink or rarely white,
the outer surface moderately to densely glandular-hairy. Stamens 5, exserted,
the filaments 4.0–4.5 cm long, arched upward, hairy toward the base, lacking
spurs near the anther-filament junction, the anthers tiny, ovate, lacking tubes
or awns at the tip, dehiscing by 2 terminal pores. Ovary superior, densely
glandular-hairy, with 5 locules, the placentation axile. Style 4–6 cm long,
arched upward or slightly S-shaped, exserted to slightly beyond the stamens,
mostly not persistent at fruiting, the stigma obconic to disk-shaped, shallowly
5-lobed. Fruits capsules, 10–14 mm long, 3–5 mm wide, narrowly oblong-ovoid to
cylindrical, sparsely to densely glandular-hairy, dehiscing longitudinally from
the tip along the sutures. Seeds 2.0–3.5 mm long, 0.6–1.0 mm wide, irregularly
ovate to elliptic, strongly flattened and irregularly winged, the wing more or
less entire at the tip and more or less fringed or dissected at the base, the
surface more or less smooth, yellowish brown to light brown, shiny. 2n=26.
April–May.
Scattered and
local in southeastern Missouri and the southern portion of the Ozark Division
(eastern U.S. and adjacent Canada west to Missouri, Oklahoma, and Texas). Mesic
upland forests and ledges of bluffs, mostly on north-facing exposures and
acidic substrates.
This species has
a disjunct distribution, occurring mainly in the Appalachians and the Ozarks.
Overall, plants in the western part of the range tend to have longer corolla
tubes than those in the eastern portion, but a number of exceptions are known
from each region (Kron, 1993). This species was known as R. roseum in
much of the older literature (Steyermark, 1963), however that name was not
validly published (Shinners, 1962; Kron, 1989).
The
morphologically similar R. canescens (Michx.) Sweet (Piedmont azalea) is
relatively widespread in the southeastern United States and has been documented
from Union County, Illinois (adjacent to Cape Girardeau County, Missouri), as
well as from several counties in western Kentucky and Tennessee. It differs
from R. prinophyllum in its shorter and usually glandless flower stalks,
narrower corolla tube expanded more abruptly into the lobes, and hairy fruits
(Kron, 1993). This species can easily be mistaken for R. prinophyllum
and may eventually be located in Missouri.