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Cactaceae


This large family is almost entirely restricted to the Americas, especially in dry, warm areas of the southern United States and Central America. No species of cactus is native to Australia, but several are introduced and some are serious weeds, mostly of drier areas in the southern and eastern states (except Tasmania).

Characteristic features of the family Cactaceae in Australia include:

  • herbs, scramblers or shrubs, usually without leaves but with fleshy, jointed photosynthetic stems (cladodes), usually with stout spines and tufts of sharp bristles in areoles
  • flowers single or clustered at the areoles (rarely in a cyme or panicle), with a tubular hypanthium and few to many free, coloured, spirally-arranged segments
  • stamens numerous
  • ovary inferior; fruit fleshy with large seeds buried in often coloured, edible flesh

Description

Evergreen, deciduous or semi-deciduous trees, shrubs, woody or herbaceous scrambling vines or perennial terrestrial herbs. Stems succulent, unarmed or with prickles or spines arising from the stem surface, rarely bearing leaves; internodes spongy, pithy, terete, oval or slightly or strongly flattened. Internal secretions not obvious. Plants glabrous or with simple, non-glandular, unicellular hairs. Leaves much reduced (i.e. to scales, etc.), falling off early or entirely absent, or rarely well-developed, alternate and spiral, cauline if herbs, sessile (when present). Stipules absent. Lamina simple, symmetric, elliptic, ovate, obovate or subulate; margins entire or ?crenate; base cuneate or rounded, ±flat; with the midrib ?conspicuous or inconspicuous, and the tertiary venation not reticulate; surfaces not punctate; succulent. Plants with all the flowers bisexual. Inflorescences axillary, consisting mostly of solitary flowers, or rarely of panicles or cymes. Bracts and bracteoles absent. Pollination by insects or bats. Flowers odourless or fragrant; sessile or stalked. Floral disc present; nectaries present on the disc. Free hypanthium present or absent. Perianth of 2 dissimilar whorls or of 1 whorl only or all whorls ±similar, with 1290 segments, imbricate in bud. Calyx regular, with 630 free sepals, herbaceous. Corolla regular or irregular; segments free or fused, with 660 petals or lobes, with no clear relationship to the sepals; corolla funnel-shaped or tubular, curved-tubular, white, cream, yellow, orange, red, pink, magenta or purple, without contrasting markings, membranous; claws absent; lobes ±entire. Fertile stamens numerous, not clearly correlated with the sepals, free or at least partly fused to the corolla, free of the ovary and style, distinct from each other, all ±equal. Anthers basifixed, versatile, opening inwards by longitudinal slits; 2-celled. Ovary part-inferior or inferior. Carpels 320, fused; ovary with 320 locules. Style terminal, single and unbranched, or single and branched above. Ovules numerous per locule, stalked; placentation basal or parietal. Fruit a fleshy, indehiscent berry; the perianth on the maturing fruit deciduous. Disseminule micro-surface ±smooth, tuberculate or reticulate, brown, grey or black, glossy or dull. Seeds numerous per fruit. Aril absent. Cotyledons 2. Embryo curved.
(Note: this description has been generated from the coded data compiled for the key. Any errors in the key data will be reflected in the descriptions.)

A treatment of the family Cactaceae has been published in:
Flora of Australia 4: 62-80.

Australian genera of Cactaceae (as recognised for the Flora of Australia)

* = all species introduced

*Acanthocereus
*Epiphyllum
*Eriocereus
*Hylocereus
*Nyctocereus
*Opuntia
*Peniocereus
*Pereskia


Acanthocereus pentagonus (branch)
Photo: S.Jacobs S.Jacobs 


Opuntia stricta (flower)
Photo: anon NSW National Herbarium 


Opuntia stricta (fruits)
Photo: G.Leiper G.Leiper