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Key to the Genera of the Cacti
- University of Texas Press
- Chapter
- Additional Information
Key to the Genera of the Cacti The keys which are given here and before the discussion of each major genus are based as far as possible on the vegetative characters of adult individuals , but it appears to be impossible to construct workable keys for the cacti based on these alone. It was found necessary to refer in some cases to the flowers or fruits and sometimes even to the seeds. This means that the keys will be less than satisfactory in certain seasons and will not identify most juvenile forms at all. Those using the keys will need to have before them very nearly complete adult specimens of the living plants. The keys are artificial and are my own. They are binomial keys, presenting a series of choices between two alternatives. In use, one reads the first choice (1a) and compares the specimen in question with the description. If the description at 1a fits the specimen, one then proceeds to the number given at the end of the description and repeats the process there. If the description at 1a does not fit the specimen, then the user abandons 1a and moves on to 1b, which is the alternate choice. If the specimen matches 1b, then one moves to the number given at the end of 1b, and so on. When this process is followed carefully with a mature plant from our area, it should lead to a description, after which a plant name and page number are given. This is the name of the specimen in hand and the discussion of it will start on that page. If at any point the specimen does not fit either the a or b choice one has arrived at, there are two possible explanations. Either the user has already made a wrong choice somewhere earlier in the process, or else the cactus is not included in the key. Careful reconsideration of all choices should show which is the case. If the user cannot choose between alternatives by studying the specimen, he or she may have to secure a more mature or more complete example in order to key the form. 1a. Stems of mature plants ribbed—that is, the surfaces of the stems covered with vertical or sometimes spiraling ridges which may be completely uninterrupted, undulate, or sometimes almost completely interrupted by grooves between the areoles, but which are never, on mature stems, rows of completely separate tubercles—2. 2a. Plants possessing spines—3. 3a. Stems of plants upright, prostrate, or clambering, with mature stems more than twice as long as they are thick; the flowers produced on the sides of the stems, with the ovary surfaces spiny; the fruit remaining fleshy and indehiscent or sometimes splitting open laterally—4. 4a. Stems not more than about 6 times as long as they are thick, not over 24 inches long, upright or prostrate, but not clambering, key to the genera of the cacti 7 often caespitose; the flowers produced from a rupture of the stem epidermis just above an areole —Genus Echinocereus (see key on page 10). 4b. Stems when mature at least 8 to sometimes 100 times as long as they are thick, on old specimens becoming more than 24 inches long, upright or clambering, never caespitose; the flowers produced from within a spine areole—5. 5a. Stems 1/4 to 1 inch in diameter; spines 1/32 to 1/4 inch long; roots tuberous—6. 6a. Stems 1/4 to 5/8 inch thick; ribs 8; spines to 1/4 or 3/8 inch long; rootsclusteringtubers;flowerspurplishwithshorttubesand opening during the day —Genus Wilcoxia (see page 79). 6b. Stems 1/2 to 1 inch thick; ribs 3 to 6; spines 1/32 to 1/8 inch long; root a single extremely large taproot; flowers mostly white with long tubes and opening at night —Genus Peniocereus (see page 82). 5b. Stems 2 to 4 inches in diameter; spines 3/8 to 2 inches long; roots fibrous —Genus Acanthocereus (see page 85). 3b. Stems of plants upright, never more than twice as tall as they are thick; the flowers produced at the apex of the stem, with the ovary surface scaly or sometimes with hair, but never spiny; the fruit opening basally or laterally —Genus Echinocactus (see key on page 91). 2b. Plants spineless—7. 7a. Flowers large and yellow with red centers; ovary scaly —Genus Echinocactus (see key on page 91). 7b. Flowers small and pinkish; fruit never having spines or scales —Genus...