Kim S C, Crawford D J, Francisco-Ortega J, Santos-Guerra A
Department of Plant Biology, Ohio State University, Columbus 43210-1293, USA.
Proc Natl Acad Sci U S A. 1996 Jul 23;93(15):7743-8. doi: 10.1073/pnas.93.15.7743.
Woody Sonchus and five related genera (Babcockia, Taeckholmia, Sventenia, Lactucosonchus, and Prenanthes) of the Macaronesian islands have been regarded as an outstanding example of adaptive radiation in angiosperms. Internal transcribed spacer region of the nuclear rDNA (ITS) sequences were used to demonstrate that, despite the extensive morphological and ecological diversity of the plants, the entire alliance in insular Macaronesia has a common origin. The sequence data place Lactucosonchus as sister group to the remainder of the alliance and also indicate that four related genera are in turn sister groups to subg. Dendrosonchus and Taeckholmia. This implies that the woody members of Sonchus were derived from an ancestor similar to allied genera now present on the Canary Islands. It is also evident that the alliance probably occurred in the Canary Islands during the late Miocene or early Pliocene. A rapid radiation of major lineages in the alliance is consistent with an unresolved polytomy near the base and low ITS sequence divergence. Increase of woodiness is concordant with other insular endemics and refutes the relictural nature of woody Sonchus in the Macaronesian islands.
加那利群岛的木质苦苣菜属及五个相关属（巴布科克苣属、泰克霍尔姆苣属、斯文特尼亚苣属、乳苣苦苣菜属和福王草属）被视为被子植物适应性辐射的一个突出例子。利用核核糖体DNA（ITS）序列的内部转录间隔区来证明，尽管这些植物在形态和生态上具有广泛的多样性，但加那利群岛的整个类群有着共同的起源。序列数据表明，乳苣苦苣菜属是该类群其余部分的姐妹群，同时也表明四个相关属依次是树苣苦苣菜亚属和泰克霍尔姆苣属的姐妹群。这意味着苦苣菜属的木质成员源自一个与现在加那利群岛上的相关属相似的祖先。同样明显的是，该类群可能在中新世晚期或上新世早期出现在加那利群岛。该类群主要谱系的快速辐射与基部附近未解决的多歧分枝以及低ITS序列分歧相一致。木质化程度的增加与其他岛屿特有植物一致，并且反驳了加那利群岛上木质苦苣菜属的残遗性质。
