CABOMBACEAE (Water Shield Family)
Alan E. Brant
herbs, with short rhizomes (seldom collected) giving rise to long (to 2 m or
more) branched stems potentially rooting at the nodes. Leaves opposite and/or
alternate, with well-developed, mostly long petioles. Stipules absent. Leaf
blades simple and entire or highly dissected. Flowers solitary in the leaf
axils, mostly long-stalked, hypogynous, perfect, actinomorphic. Perianth showy,
appearing free, the sepals and petals fused only at the very base, persistent
at fruiting. Sepals 3 or 4. Petals 3 or 4. Stamens 3–6 or numerous, free,
the filament slender and flattened, attached at the anther base. Pistils
(1–)2–18, each with 1 carpel, the ovary superior, with
1–5 ovules. Style 1, the stigma capitate or a linear region toward the
style tip. Fruits in a ring or cluster, achenelike, indehiscent, leathery.
Seeds 1–3. Two genera, 6 species, worldwide.
Cabombaceae were included in the Nymphaeaceae by Steyermark (1963) and other
earlier authors, but most botanists now agree that Cabomba and Brasenia
constitute an independent family, based on a variety of morphological and
biochemical characters. Both groups comprise aquatics with submerged and/or
floral biology of the two species present in Missouri has been studied in
detail (Schneider and Jeter, 1982; Osborn and Schneider, 1988). Brasenia
schreberi is primarily wind pollinated, and although a number of bees and
wasps visit the flowers of Cabomba caroliniana, it is mainly
fly-pollinated. In both species, individual flowers are open for only two days.
On the first day, the stigmas become receptive as the flower opens at
mid-morning; in the late afternoon, the flower closes and the flower stalk
bends, resulting in the submergence of the flower overnight. On the second
morning, the flower emerges from the water again, and although the stigmas are
no longer receptive, the stamens elongate slightly and shed their pollen. The
second evening, the flower again closes and become submerged, with fruit
development occurring underwater. Thus, first-day flowers are cross-pollinated
with pollen from second-day flowers.