Cactaceae Juss.

Zappi, D. (2009). Neotropical Cactaceae.

Morphology

Description

Trees, shrubs or herbs, sometimes epiphytes, with three distinct types of branch: normal vegetative branches, areoles (reduced branches that can originate stems, spines or flowering branches) and flowering branches. Developed leaves present in one subfamily (Pereskioideae), reduced leaves present in Opuntioideae, Cactoideae devoid of leaves. Branches green, photosynthetic, succulent , ribs and tubercles present. Spines organized within areoles, together with hairs and bristles, specialized serrated spines and glochid present only in Opuntioideae. Flowers generally showy, epigynous , with receptacular inferior ovary , solitary or in inflorescences, externally with areoles, bracts and many perianth segments arranged spirally and showing a transition between sepaloid (external) and petaloid (internal) segments, flower tube generally developed, nectar chamber above the ovary and basal region of the tube, stamens numerous, filaments fleshy ; ovary unilocular, originated from the fusion of many carpels (generally number of carpels reflected in the number of stigma lobes). Fruits berry -like, fleshy , multi-seeded, indehiscent or dehiscent , seeds cochleariform, with bone-like testa in Opuntioideae, testa dark and normally shiny in Pereskoideae and Cactoideae.

Distribution

Distribution in the Neotropics

• Neotropical distribution with the exception of one species, Rhipsalis baccifera (J.S.Mill.) Stearn, distributed in the Old World.

Diagnostic

Other important characters

• Succulence.
• Spines.
• Many perianth transitional segments (sepals and petals).

Key differences from similar families

• Rarely present latex (different from succulentEuphorbiaceae).
• Spines are produced in areoles (different from other stem succulents like Asclepiadaceae, Euphorbiaceae, etc.).

Notable genera and distinguishing features

• Cereus Mill.: Tree-like with naked large nocturnal flowers and fruits dehiscent by longitudinal slits, 30+ species mostly S. American.
• Pilosocereus Byles & G.D.Rowley: Shrubby to tree-like with nocturnal, dull, smelly flowers and fruits subglobose dehiscent by irregular slits, 30+ speices mostly S. American.
• Melocactus (L.) Link & Otto: Globose, with cephalium and small diurnal red, pink or magenta flowers, fruits white to deep red, 30+ species South American and Caribbean. 
• Epiphyllum Haw.: Foliose, epiphytic with showy, large flowers, 15+ species mostly Caribbean.   
• Rhipsalis Gaertn.: Epiphytic, string-like, with small white flowers without tube and fleshy fruits, 30+ species, mostly Brazilian Atlantic forest.   
• Mammillaria Haw.: Small globose to cylindric, with tubercles and two different types of areoles, latex sometimes present, small flowers appearing in rings around the stem, 50+ species mostly Mexican. 
• Echinopsis Zucc.: Variable habit from tree-like to globose, large flowers white to deep red, externally with areoles and hairs, 50+ species mostly Andean.  
• Parodia Speg.: Globose to cylindric, flowers diurnal yellow to red or pink, short tube.
• Opuntia Mill.: Shrubs to tree-like plants with reduced, scale-like leaves and flattened pads with glochids and serrate spines, flower with well defined green pericarpel, no tube, sensitive stamens, c. 200+ species mostly Caribbean and North American.
• Pereskia Mill.: Trees or climbers with well developed leaves, flowers without developed tube, white, orange, pink or red, fruits indehiscent with large seeds, c. 18 species South American and Caribbean.

Useful tips for generic identification

First subdivide in Subfamilies:

• Opuntioideae have bony seeds, serrated spines and glochids.
• Pereskoideae have really well developed leaves and are not very succulent.
• Cactoideae are stem succulents without leaves, with black shiny seeds.

Useful characters to define tribes/genera:

• With or without conspicuous areoles.
• Presence/absence of ribs.
• Flowering structure (cephalium).
• Fruits (aspect, dehiscence).
• Seed characters.

Distinguishing characters (always present)

• Presence of three types of branches: vegetative expanded branches, reduced structure bearing branches called areoles (specific to the family), flowering branches.
• Receptacular inferior ovary.
• Spines (sometimes lacking or profoundly modified).

General Description

Number of genera

• 124 genera, over 1,300 species.

General notes

The three main centres of diversity of this largely Neotropical family are the highly endemic drylands of Mexico, the Argentinian/Bolivian Andes and Eastern Brazil. A large proportion of the species are endemic to deserts and arid regions, but there are also epiphytes in the wettest forests of the Neotropics. The taxonomy of this family has been shaped by the important contribution of amateurs, who discovered and described a large number of species, many of them in cultivation nowadays.

Status

• Cultivated under glass in temperate regions, naturalised outdoors in the Paleotropics (in Australia some Opuntia became weeds), especially Opuntia ficus-indica Mill. (from Mexico but widely cultivated and introduced in Mediterranean regions, nowadays part of the culture in Europe); endemic species are endangered through habitat destruction and modification (agriculture, irrigation) and, to a lesser scale, by overcollection by amateurs.

Notes on delimitation

• DNA studies show that Portulacaceae possibly cannot be separated from Cactaceae because it lacks autoapomorphies; Cactaceae however presents areoles which are not present as such in Portulacaceae.

Literature

Important literature

Hunt, D., Taylor, N., Charles, G. 2006. The New Cactus Lexicon. 2 vols.

Cactaceae, R. Hunt. Flora of Tropical East Africa. 1968

Morphology General Habit

Highly specialized fleshy perennials of diverse habit

Morphology Stem

Stems terete, globular, flattened or fluted, mostly leafless and variously spiny; spines always arising from complex axillary structures (areoles)

Morphology Reproductive morphology Flowers

Flowers solitary or rarely clustered, sessile (except in Pereskia), almost always bisexual, usually regular

Morphology Reproductive morphology Flowers Perianth

Perianth segments ?, closely imbricated in bud, in a sepaloid to petaloid series, ± free or fused below to form a short or elongate tube (hypanthium)

Morphology Reproductive morphology Flowers Androecium

Stamens ?; filaments variously inserted on or at base of perianth; anthers 2-thecous, splitting longitudinally

Morphology Reproductive morphology Flowers Gynoecium

Ovary almost always inferior, with 3–? parietal placentas; ovules ?; style single; stigma-lobes 3–?

Morphology Reproductive morphology Fruits

Fruit a dry or juicy berry, often spiny, bristly or scaly

Morphology Reproductive morphology Seeds

Seeds ?, variously arillate or carunculate, with or without endosperm; embryo straight or curved

Distribution

A large, almost exclusively American family, several of whose members are grown as ornamentals in East Africa. The epiphytic genus >i>Rhipsalis is sometimes considered to be indigenous in Africa, and a number of >i>Opuntia species have become widely naturalized

Cactaceae, Hutchinson and Dalziel. Flora of West Tropical Africa 1:1. 1954

Morphology General Habit

Succulent herbs and shrubs of diverse habit, often very spiny, and usually with much reduced leaves

Morphology Reproductive morphology Flowers

Flowers hermaphrodite, actinomorphic, often handsome, but very small in the African species (Rhipsalis)

Morphology Reproductive morphology Flowers Calyx

Calyx-tube adnate to the ovary and often produced beyond; lobes few to many, or reduced to minute teeth

Morphology Reproductive morphology Flowers Corolla

Petals 6 or more

Morphology Reproductive morphology Flowers Androecium

Stamens numerous, free or adnate to the base of the petals

Morphology Reproductive morphology Flowers Gynoecium

Ovary inferior, 1-celled, with parietal many- or rarely few-ovuled placentas; stigma usually radiate

Morphology Reproductive morphology Fruits

Fruit baccate, many-seeded

Morphology Reproductive morphology Seeds

Seeds mostly without endosperm