Key to Genera

Leaves broad and flat 1. Pereskiopsis

Leaves subulate or cylindric.

Seeds broadly winged 2. Pterocactus

Seeds wingless.

Stamens much longer than the petals.

Petals erect; joints flat 3. Nopalea

Petals recurved; joints terete 4. Tacinga

Stamens shorter than the petals. Joints flat to terete, not ribbed.

Testa of the seed thin, black, shining 5. Maihuenia

Testa thick, pale, dull 6. Opuntia

Joints terete, longitudinally ribbed 7. Grusonia

1. PERESKIOPSIS Britton and Rose, Smiths. Misc. Coil. 50: 331. 1907.

Trees and shrubs, in habit and foliage similar to Pereskia; old trunk forming a solid woody cylinder covered with bark and resembling the ordinary dicotyledonous stein; areoles circular, spine-bearing or sometimes spineless, also bearing hairs, wool, and usually glochids; flowers similar to those of Opuntia; ovary sessile (one species described as pedunculate), with leaves at the areoles (except in one species); fruit red, juicy; seeds bony, few, covered with matted hairs.

Type species: Opuntia brandegeei Schumann.

The plants are common in hedges and thickets of Mexico and Guatemala.

As to the number of species to be recognized in this genus we are uncertain; about 16 have been described. In our first discussion of the genus (op. cit.) we recognized 11 species, including several known only from descriptions. There now seem to be at least 10 species, of which 8 are in cultivation in Washington and New York. Two of the plants were described, as early as 1828, as species of Pereskia, and here they remained with 2 later-described species until, in 1898, Dr. A. Weber transferred them to Opuntia, placing them in a new subgenus, Pereskiopuntia. The same year Dr. Karl Schumann adopted Weber's conclusions, publishing his treatment of the subgenus and assigning 5 species to it.

In its large leaves and woody, spiny stems, this group suggests Pereskia, but it has glochids and different flowers, fruit, and seeds; in flowers, fruit, seeds, and glochids it resembles Opuntia, but on account of habit and foliage must be excluded from that genus.

In view of these differences, Britton and Rose in 1907 established the genus Pereskiopsis and listed 11 species, 4 of which had been originally described as species of Pereskia and 5 as species of Opuntia. Since then we have grown most of these plants along with the pereskias and opuntias so as to compare them. Unfortunately we are not able to describe all the species fully, for they have never been known to flower in cultivation, although some of the species, at least, bloom freely in the wild state. The leaves on the lower parts of shoots are sometimes broader and shorter than those on the upper parts, and in greenhouse cultivation the leaves of some species are narrower than when the plants, are growing under natural conditions.

The generic name is from the Greek and signifies resembling Pereskia.

Continue reading here: Key to Species

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