Department of Plant Biology, University of Minnesota, St. Paul, Minnesota 55108 USA;
Am J Bot. 2004 Jun;91(6):905-17. doi: 10.3732/ajb.91.6.905.
The Begoniaceae consist of two genera, Begonia, with approximately 1400 species that are widely distributed in the tropics, and Hillebrandia, with one species that is endemic to the Hawaiian Islands and the only member of the family native to those islands. To help explain the history of Hillebrandia on the Hawaiian Archipelago, phylogenetic relationships of the Begoniaceae and the Cucurbitales were inferred using sequence data from 18S, rbcL, and ITS, and the minimal age of both Begonia and the Begoniaceae were indirectly estimated. The analyses strongly support the placement of Hillebrandia as the sister group to the rest of the Begoniaceae and indicate that the Hillebrandia lineage is at least 51-65 million years old, an age that predates the current Hawaiian Islands by about 20 million years. Evidence that Hillebrandia sandwicensis has survived on the Hawaiian Archipelago by island hopping from older, now denuded islands to younger, more mountainous islands is presented. Various scenarios for the origin of ancestor to Hillebrandia are considered. The geographic origin of source populations unfortunately remains obscure; however, we suggest a boreotropic or a Malesian-Pacific origin is most likely. Hillebrandia represents the first example in the well-studied Hawaiian flora of a relict genus.
秋海棠科包含两个属，秋海棠属，约有 1400 种，广泛分布于热带地区；以及异檐果属，仅有 1 种，是夏威夷群岛的特有种，也是该家族在这些岛屿上的唯一成员。为了帮助解释夏威夷群岛上异檐果属的历史，使用来自 18S、rbcL 和 ITS 的序列数据推断了秋海棠科和葫芦科的系统发育关系，并间接估计了秋海棠属和秋海棠科的最小年龄。分析结果强烈支持将异檐果属置于秋海棠科的姊妹群位置，并表明异檐果属的谱系至少有 5100 万到 6500 万年的历史，比当前的夏威夷群岛早约 2000 万年。本文提出了异檐果属沙威氏种通过从较老、现已光秃的岛屿跳跃到较年轻、多山的岛屿，在夏威夷群岛上幸存下来的证据。考虑了起源于异檐果属祖先的各种情景。遗憾的是，其源种群的地理起源仍然不清楚；然而，我们认为起源于北热带或马来-太平洋地区的可能性最大。异檐果属代表了在研究充分的夏威夷植物群中，第一个遗留属的例子。
