CACTACEAE (Cactus Family)
(Benson, 1982;
Anderson, 2001)
Ninety-three to
125 genera, 1,400–1,850 species, North America to South America, Caribbean
Islands; 1 species in Africa, Madagascar.
The morphology
of cactus plants requires some explanation. Except for the relatively primitive
genus Pereskia Mill., which includes more or less normal-looking spiny
shrubs and trees with well-developed leaves, in cacti the stems have become
modified and thickened to serve in photosynthesis and water storage, whereas
the leaves are essentially absent or very short-lived. There is a bewildering
diversity of stem shapes, sizes, surface textures, and branching patterns in
the family. The spines of cacti are produced on areoles, which can be thought
of as extremely short, highly modified branches. Spines actually develop from
the axillary buds associated with the numerous closely spaced nodes of the
areole and often appear to have a more or less radial distribution on the
areole. Flowers also are produced in association with areoles and
developmentally are thus considered to be axillary and solitary (except in Pereskia).
Most species produce flowers with numerous perianth parts that grade
continuously from sepaloid to petaloid morphology along the densely spiraled
series and thus are referred to as tepals. Taxonomically, the family is
considered to represent a morphologically specialized offshoot of the
Portulacaceae (Hershkovitz and Zimmer, 1997; Applequist and Wallace, 2001) and
to have experienced an explosive radiation of species in the New World, with
the result that many of the species are difficult to distinguish from others
within a given complex. This has led to great controversy as to species numbers
and delimitation in most of the larger genera (generic delimitation has been
equally contentious). In an effort to stabilize the nomenclature and taxonomy
of the family, since 1984 an International Cactaceae Systematics Group of
specialists has worked to produce a consensus classification and checklist
(Hunt, 1999) for use by horticulturalists, conservation officers, and others
interested in the family.
With their
unusual stems and bright flowers, cacti are popular both among amateur
enthusiasts and botanists. In fact, there is a huge horticultural market for cacti,
which also have economic importance as landscape plants in dry and seasonally
dry regions of the United States and other countries. Overcollection from the
wild for horticultural purposes has led to the endangerment of numerous
species, thus international trade in most cacti is closely regulated by the
Convention on International Trade in Endangered Species of Wild Fauna and Flora
(CITES). Some species of cacti, particularly members of Opuntia and
related genera, also are cultivated for their edible fruits and stems and as
hosts for homopteran cochineal insects (Dactylopius spp.), which produce
a beautiful red dye. Other genera, particularly peyote (Lophophora
williamsii (Lam. ex Salm-Dyck) J.M. Coult.), have been cultivated and/or
wild-harvested for their hallucinogenic properties. The wood of various cacti
sometimes is used in handicrafts. Cactus spines can cause damage to the legs,
feet, and mouthparts of livestock, and some cacti have been considered pest
plants in pastures. This is especially true in Australia, where imported Opuntia
species rendered millions of acres of rangeland unfit for livestock and other
uses until biological controls involving stem-boring larvae of the South
American moth genus Cactoblastus proved effective.
In addition to the
numerous species cultivated in homes, greenhouses, and conservatories, several
nonnative cacti are cold-hardy in Missouri’s climate and are cultivated
outdoors as specimen plants in well-drained soils. These generally have not
escaped into the wild, but they occasionally persist at old homesites. The best
example of this is a tree cholla, Cylindropuntia imbricata (Haw.) F.M.
Knuth (Opuntia imbricata (Haw.) DC., O. arborescens Engelm.),
which is native from Colorado to Kansas south to Texas and Mexico. A single
individual of this species was located in 1998 by an amateur botanist, T.
Owens, in Laclede County growing on a dry ridgetop overlooking the Niangua
River. This species has cylindrical stems to 2 m tall and 3 cm in diameter that
are covered with coarse, elongate tubercles and dense clusters of spines. The
stems are jointed every 5–35 cm and have whorled branches. The flowers have
bright pink to reddish purple tepals to 5 cm long, and the broadly obovoid
fruits are spineless and more or less yellow at maturity. This species
eventually may need to be added to the roster of the state’s flora and should
be searched for, especially in the Unglaciated Plains Division.
Beginning with
an unsubstantiated listing from Pulaski County (Palmer and Steyermark, 1935),
there also have been persistent anecdotal reports (mostly from western
Missouri) of another regionally native cactus species, Escobaria
missouriensis (Sweet) D.R. Hunt (Mammillaria missouriensis Sweet, Coryphantha
missouriensis (Sweet) Britton & Rose; Neobesseya missouriensis
(Sweet) Britton & Rose, Neomammillaria missouriensis (Sweet) Britton
& Rose, Neomammillaria similis (Engelm.) Britton & Rose), which
is known by various common names, including ball cactus, beehive cactus, cream
cactus, and Missouri pincushion cactus. Its distributional range stretches from
Idaho to Arizona east to North Dakota, Kansas, and Texas (also adjacent
Mexico). Steyermark (1963) excluded it from the Missouri flora, but searches of
thin-soil areas of prairies, glades, and bluff tops may result in its eventual
documentation from the state. Escobaria missouriensis produces small,
globose to broadly obovoid stems, these 2–5 cm long, solitary or forming small,
clustered mounds, and covered with nipplelike tubercles tipped with a dense
cluster of short, straight spines. The flowers have narrow tepals 1–2 cm long
that are cream-colored to light yellow or greenish yellow, often reddish- or
pinkish-tinged toward the base. The globose to obovoid fruits are 1–2 cm long,
spineless, and bright red at maturity.