Molecular phylogeny and comparative ecology of Mexican Stevia

墨西哥甜叶菊包括大约100种一年生、多年生和灌木，其中灌木物种被认为是祖先。不同物种的花形态是不同的。自交配子和无融合生殖存在于许多物种中。染色体数目从n=11到n=12不等。本项目的目标是检查世代时间、生殖系统、花形态和染色体数目之间的相关性。为了获取研究材料，我们在墨西哥进行了实地考察。1995年，我们在瓦哈卡、韦拉克鲁斯、哈利斯科等州进行了实地考察。我们收集了近50种甜叶菊，其中包括甜叶菊和甜叶菊，它们在过去的一百年里从未被采集过，被认为已经灭绝。我们还发现了几个新物种。1996年，我们到恰帕斯州、奇瓦瓦州、杜兰戈州和其他一些北部州进行了实地考察。作为两年实地考察的结果，我们获得了100种植物中约80种的材料。对这些材料进行的染色体计数表明，灌木种12种，多年生种12或11种，一年生种11或4种。这一事实支持了染色体数量减少与世代时间减少相关的观点。所研究的灌木和一年生植物材料均为有性二倍体，而多年生植物通常为三倍体、四倍体或五倍体，被认为是种子无融合生殖。根据ITS序列分析，灌木状种(n=12)是该属的单系和基生种，多系种属于两个单系群，其中包括三角链霉菌(S.deltoidae，n=12)和地锦链霉菌(S.decummbens，n=12)，另一种包括一些种(n=11，11，12)。

Mexican Stevia includes about 100 species of annual, perennial, and shrubs among which shurubby species are considered to be ancestral. Floral morphology is diversified among species. Autogamy and apomixis are found in many species. Chromosome numbers vary from n=11 to n=12.The goal of this project is to examine correlation in generation time, reproductive system, floral morphology and chromosome numbers. To obtain research materials, we carried out field trips in Mexico.In 1995, we had field trips in Oaxaca, Veracruz, Jalisco and some other states. We collected about 50 species of Stevia including Stevia phlebophyla and S.karwinskyana which had never been collected during the past hundred years and had been considered to be extinct. We also found several new species. In 1996, we had field trips to Chiapas, Chihuahua, Durango and some other northern states. As a result of field trips during the two years, we obtaiened materials of approximately 80 species of the 100 total. Chromosome counts made on these materials revealed that shrubby species have n=12, perennial species have n=12 or 11, and annual species have n=11 or 4 (in S.ephemera). This fact supports the idea that chromosome number reduction is associated with reduction in generation time. All materials of shrubs and annuals examined were sexual diploids while perennial plants are often triploids, tetraploids or pentaploids and are regarded as seed apomicts.As a result of a phylogenetic study using sequences of matK,Carphocaete (n=12) was shown to be a sister genus of Stevia. Another study using sequences of ITS revealed that shurubby species (n=12) are monophyletic and basal in the genus ; perrenial species belong to two monophyletic groups, one of which includes S.deltoidea (n=12) and S.decummbens (n=12), and the other includes some species with n=11 and S.origanoides (n=11,12).