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Kalanchoe: The Genus and its Chromosomes

J. T. Baldwin, Jr.
American Journal of Botany
Vol. 25, No. 8 (Oct., 1938), pp. 572-579
Stable URL: http://www.jstor.org/stable/2436516
Page Count: 8
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Kalanchoe: The Genus and its Chromosomes
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Abstract

Evidence from taxonomy, embryology, and cytology indicates that the Kalanchoideae are a well-defined group in which relationships are intimate. Within this complex it is difficult to make morphologically precise segregations on a generic level. It seems proper, therefore, to follow those systematists who reduce Bryophyllum and Kitchingia to Kalanchoe and thus to recognize a single genus for the subfamily. Kalanchoe, as considered here, includes about 125 species; chromosome numbers have been determined for approximately a fourth of them. The chromosomes are small throughout the genus; their characters are of slight taxonomic value. The numbers determined are inferred to belong to a primary system of 17 and secondary systems of 18 and 20. Reasons for this inference are several: preponderance of 2n-numbers divisible by 17, specialized characters in the species presumably derived from the 17-trend, and a more close (probably secondary) association of bivalents in species with gametic numbers of 20, 36, and 51 than in those with 17. Polyploid forms were found in the 17- and 18-systems. The generic lines that have been proposed for this Kalanchoe-aggregate do not coincide with these trends in the chromosomal development of the group. A 2n-number of ca. 500 is estimated for one of the species. Cuttings of this species produce roots sparingly; the situation is unusual for the family. The initial basic number for the Crassulaceae is deduced to be 4. Many interfusing chromosomal trends are distinguishable in the family. The taxonomic complexity of the group thus has a karyological parallel. It is implied that the ability of the family to propagate itself so well by non-sexual means has been an important factor in the attainment of its present cytological state. The suggestion is offered that Kalanchoe might have originated from a hybrid of species representing two other subfamilies with subsequent amphidiploidy. A similar suggestion has been made for the origin of Pomoideae. A taxonomic key to some of the kalanchoes in the American trade is included.

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