Typhonium jinpingense Z.L.Wang, H.Li & F.H.Bian

Typhonium is commonly accepted as comprising five sections as described by Sriboonma et al. (1994). This new species belongs to section Typhonium. From the shape of the leaf blade, this new species is easily differentiated from the other Chinese Typhonium species, except T. blumei. It is distinguished from T. blumei in having the spathe tube pale green, dark purple at the top (not entirely dark purple), the blade narrowly lanceolate (not broadly ovate), dark purple, spreading and arching, apex long acuminate but not twisted, clavate sterile rudiments, erect, and in its chromosome number, 2n = 10.
Based on recent comprehensive reviews of the cytology of the Araceae (Grayum, 1990; Mayo et al., 1997; Petersen, 1989, 1994), the chromosome numbers vary greatly between and also within genera, from 2n = 14 (Ulearum) to 2n 5 168 (Arisaema).
The lowest diploid number so far known in Araceae is 2n = 14, observed in Ulearum sagittatum Engler; based on our results, Typhonium jinpingense (2n = 10) has the lowest chromosome number known to occur in the family. The chromosomes were easy to group into five pairs (Fig. 2), so Typhonium jinpingense is a diploid species and the basic chromosome number is 5. Other species of Typhonium have chromosome numbers of: 2n = 16, 18, 20, 26, 36, 52, 54, 65, .100 (Mayo at al., 1997), making it one of the most variable genera in this regard in Araceae.
Primary basic chromosome number is a main area of research in cytological studies. The discovery of the lowest diploid number in this study may spur further investigation of this aspect. Possibly the following questions will be proposed: Was it caused by extreme aneuploid reductions? Or is 2n = 10 some kind of ‘‘ancestral number’’ only kept in Typhonium? We think the former is more likely. It is well known that very low chromosome numbers (as well as very high ones) are more common in advanced genera than in basal ones. Petersen (1994) postulated that very low chromosome numbers were explained as aneuploid reductions, from an ancestral number x = 12 or 14. Other authors proposed that there was an ‘‘original’’ series with x = 5, 6, 7, 8, and 9, and that all arose from 7 as they speculated the primary basic number as 7 (Jones, 1957; Larsen, 1969; Marchant, 1973). As stated by Mayo et al. (1997), reduction in diploid number occurs in various morphologically advanced genera. We agreed with this opinion: Typhonium is a much advanced genus in Araceae; such a low chromosome number was possibly reduced from a higher one. Other evidence came from our recent cytological studies in 9 Typhonium species. The chromosome number in somatic cells of these species is from 10 to 52, the karyotypical asymmetry for T. giganteum Engler belongs the 2A type, and 6 species, T. calcicolum C. Y. Wu, T. kunmingense H. Li, T. blumei, T. trilobatum (L.) Schott, T. roxburghii Schott, and T. omeiense H. Li, belong to the 2B type, while T. jinpingense and triploid T. flagelliforme (Loddiges) Blume, 2n = 3x 5 24, belong to the 3B type. It is commonly known that the more asymmetric the chromosome, the more advanced the species (Stebbins, 1971). The 3B type is more asymmetric than the 2A type and the 2B type. So, from the standpoint of karyotype, T. jinpingense and triploid T. flagelliforme may be considered to be the most advanced among the 9 Typhonium species studied.
Jinping County is an interesting place for the cytological study of Typhonium, as well as of the family Araceae. In addition to the new species with its low chromosome count, triploid T. flagelliforme 2n 5 3x 5 24 was also found in this county, and the latter can easily be propagated by the stem, but is not yet found to bear fruits both in the wild and in the garden.