GENERIC RELATIONSHIPS OF DECASCHISTIA (MALVACEAE) AND THE DESCRIPTION OF A NEW TRIBE, DECASCHISTIEAE

The Asiatic genus Decaschistia has traditionally been placed in the tribe Hibisceae, but it is shown that this genus has a combination of characters that does not permit it to be accommodated either in the Hibisceae or in any other tribe of the Malvaceae. A new tribe, the Decaschistieae Fryx., is therefore described and distinguished from the other four tribes currently accepted in the Malvaceae. TAXONOMISTS currently recognize four tribes in the Malvaceae (cf. Kearney, 1951; Fryxell, 1968; Bates, 1969; Bates and Blanchard, 1970). The distinguishing characters of these tribes are presented in Table 1. Although exceptions are known for certain of the characters given in the table, these exceptions do not detract from the conclusion that the tribes are natural groups. The last three characters in the table have essentially no exceptions and provide definitive bases for delimiting the four tribes. The tribe Malveae Endl. is uniquely distinguished by the absence of apical teeth on the staminal column. The tribe Gossypieae Alef. is unique among the Malvaceae in its possession of gossypol glands as well as in its embryo morphology (Fryxell, 1968). The tribe Ureneae Benth. & Hook. is distinguished by its ratio of two styles per carpel, which relationship is one-to-one in all other Malvaceae. There remains the tribe Hibisceae Reichenb. emend. Alef., which is distinguished not by any single character but by a combination of characters. This paper concerns itself primarily with the last two tribes and with the proper tribal placement of the genus Decaschistia. OBSERVATIONs-Decaschistia comprises about 16 species, most of which are native to the Indochina peninsula (Gagnepain, 1907, 1945). Two species occur in western India; on the east, one species is known from Hainan. Recently, two taxa have been described from northernmost Australia (Fryxell, 1974), but a considerable disjunction separates the Indochinese and Australian representatives of the genus. The species of Decaschistia are typically perennial shrubs, but they may sometimes be herbaceous perennials. Their flowers are relatively large and showy and superifically resemble those of Hibiscus. It may be for this reason, coupled with 1 Received for publication 21 January 1974. the lack of a critical revision of Decaschistia, that the genus has traditionally been placed in the Hibisceae (e.g., Masters, 1872; Schumann, 1890; Hutchinson, 1967), together with such genera as Hibiscus and Kosteletzkya Presl. What has generally been overlooked is that Decaschistia shares as many characters with the Ureneae (including, for example, Urena, Pavonia Cav., and Malachra L.) as it does with the Hibisceae. I have seen several herbarium specimens of Decaschistia that bear tentative determinations of "Urena sp.," indicating that others have perceived this similarity. The correct generic relationship is thus brought into question. The gynoecium-Figure 1 compares Decaschistia diagrammatically with these two tribes for certain key reproductive characters. It may be seen that Decaschistia resembles the Hibisceae in style-carpel ratio; it resembles the Ureneae in number of styles and stigmas; and it differs from both in the number of carpels per fruit. Its overall pattern is distinctive and fits none of the currently recognized tribes: ten (or sometimes fewer) carpels with an equal number of styles and stigmas. The fruit cross sections indicate the nature of dehiscence and the number of seeds per carpel. It should be noted that in the Hibisceae the number of seeds per locule varies and may sometimes be one by reduction. In the Ureneae fruit dehiscence is septicidal; the one-seeded mericarps separate from the column and from each other. There may be limited or delayed loculicidal dehiscence, but the fruit is basically schizocarpous, and the disseminule is the mericarp. In the Hibisceae, on the other hand, dehiscence is loculicidal, and the fruit is a unitary capsule, the carpel walls remaining firmly attached to the central column. The seeds are disseminated individually. Dehiscence in Decaschistia is loculicidal, as in