Integrative Biology 335:
Systematics of Plants

Families of the Caryophyllales:
Cactaceae


Readings:

Judd et al., 3rd ed., Plant Systematics: A Phylogenetic Approach (pp. 330 – 332)

Other Resources:

Digital Flowers: Cactaceae

Cactus in Wikipedia. A web article about the cactus family containing tons of information.


Cactaceae (Cactus Family)

Habit:

A cactus glochid, close up

Prickly pear cactus pads, most tender and juicy in the spring!
Nopales from Wikipedia, showing when adult pads are ready to eat. Remove the spines!

Leaves:

Flowers:

Inflorescence:

Fruits:

How to eat a prickly pear fruit on YouTube
Dragon Fruit (or pitayas, from the genus Hylocereus)

Cactaceae Class Notes

Cactaceae Illustrations from W. Zomlefer, Guide to Flowering Plant Families, page 59

Fig. 9.51 from Judd et al. text

Examples:


Cacti show numerous specializations for survival in dry and hot environments:

(1) Thick cuticle with waxy coating and sunken stomata; (2) cylindrical or spherical photosynthetic stems (large volume to surface ratio) with water storage tissue; (3) reduced leaves (spines), sometimes microscopic; (4) widespread and shallow root system, with sometimes a deep taproot; (5) spines condense dew and protect plant; (6) short growing season and long dormancy; and (7) Crassulacean Acid Metabolism (CAM). CAM permits CO2 to be absorbed at night (when stomates are open) for use in photosynthesis during the day. When stomates open, water vapour is lost.

There are varying numbers of genera and species:

In the family Cactaceae, why 20-2000 genera? Why up to thousands of species? (1) Lack of adequate material (and very difficult to make good herbarium specimens!); (2) Different parts of the same species may be treated differently; (3) Lack of characters; (4) Variation in interpretation of taxonomic boundaries (splitters versus lumpers); and (5) Amateur botanists. In general, confusion in classification exists because of: (1) Choice of characters; (2) Interpretation of characters; (3) Taxonomic opinion; (4) Tradition; (5) Method of classification; (6) Convergent evolution of similar attributes; and (7) Genetic/environmental variation.


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