CAMPANULACEAE (Bellflower Family)
Contributed by
David J. Bogler
Plants mostly
perennial herbs (sometimes shrubby elsewhere), usually with milky sap. Leaves usually
alternate, simple, the margins entire, toothed, or lobed, lacking stipules.
Inflorescences terminal spikes or racemes, axillary clusters or solitary
flowers, or the flowers rarely terminal and solitary. Flowers perfect,
epigynous or deeply perigynous. Calyces 5-lobed (sometimes 3- or 4-lobed in
cleistogamous flowers), usually actinomorphic, fused to the ovary, the tube
sometimes extending slightly past the ovary, persistent, sometimes with a
short, reflexed appendage between each of the lobes. Corollas more or less
5-lobed, actinomorphic and funnel-shaped to bell-shaped or saucer-shaped, or
zygomorphic and strongly 2-lipped, and usually split along the apparently upper
side (through which the stamens and style are exserted), white to purple, blue,
or red. Stamens 5, the filaments distinct or united into a tube toward the tip.
Anthers attached at their bases, distinct or fused into a tube surrounding the
style. Pistil 1 per flower, of 2–5 fused carpels. Ovary inferior or less
commonly only partially inferior, with 1 or 2–5 locules, the placentation
parietal (if 1 locule) or axile. Style 1 per flower, elongate, the stigma 2–5-lobed.
Ovules numerous. Fruits capsules, dehiscing by apical or lateral pores, slits,
or longitudinally. Seeds numerous, minute. Sixty to 70 genera, about 2,000
species, nearly worldwide.
The
Campanulaceae are recognized by the combination of alternate leaves, milky
latex, well-developed corolla with united petals, inferior to half-inferior ovary,
often specialized pollination mechanisms, and capsular fruits with numerous
seeds. The family comprises two distinct subfamilies that some authors have
maintained as separate families (Rosatti, 1986). The subfamily Campanuloideae
has actinomorphic flowers, nontwisted flower stalks, most commonly three
carpels and stigma lobes, free filaments and anthers, and pollen grains with
spiny ornamentation. The Lobelioideae have strongly zygomorphic flowers borne
on a stalk that is twisted so that the upper lip of the flower is positioned
basally at flowering (resupinate, as in most orchids), most commonly 2 carpels
and stigma lobes, the filaments fused into a tube toward the tip, the anthers
fused into a ring, and pollen grains with a network of ridges rather than
spines. Recent molecular studies (Cosner et al., 1994) have supported
maintaining both groups as a single family. The flowers of species in the
Lobelioideae are functionally similar to those of the Asteraceae in that the
stigma elongates through the center of the ring of fused anthers, with a brush
of hairs near the style tip pushing the pollen out of the flower, and the
stigma lobes do not spread and become receptive until after the pollen has been
released. This mechanism promotes outcrossing between flowers.
The genus Sphenoclea
is sometimes included in the Campanulaceae. The present treatment follows that
of Rosatti (1986) in treating this group as a separate family, Sphenocleaceae
(to be included in the third volume of the present work). Steyermark (1963)
noted the existence of a specimen of the commonly cultivated ornamental, Platycodon
grandiflorum (Jacq.) A. DC. (balloon flower), at the herbarium of William
Jewell College, Liberty, Missouri, but excluded the species from the Missouri
flora in the belief that it was an isolated, nonpersistent escape from an
adjacent planting. This specimen was not examined during the present study. Platycodon
resembles Campanula but differs in its larger flowers (corollas to 45 mm
long) and strongly inflated buds. It has been recorded as an escape
sporadically from New York to North Carolina, but it has not persisted outside
of cultivation yet in any midwestern state.