Two Japanese fir species (Pinaceae), Abies firma and A. homolepis, comprise the majority of the temperate forest vegetation zones of Japan. Their vertical distributions are exclusively segregated: A. firma occurs in low elevations and A. homolepis occurs in elevated regions; they contact each other at an altitude of around 1,000–1,100 m. Around the contact zone, A. umbellata is described as a tree with shoots of A. homolepis. It has the greenish cones of A. firma instead of the violet A. homolepis cones. An albinism hypothesis and a hybrid hypothesis were proposed to explain the origin of A. umbellata, provoking long debates. Therefore, we examined a total of 78 A. firma and A. homolepis trees (including an A. umbellata tree) along the altitudinal gradient in two study sites using 13 nuclear microsatellites and a species‐specific chloroplast DNA (cpDNA) marker and examined morphologies of shoots and cone scales. Finally, we tested the two hypotheses. The genetic analyses revealed that shoot morphologies of A. homolepis and A. firma correspond mostly to the genetic identity of the species, whereas nine trees with intermediate shoot morphologies and two trees (including the A. umbellata tree) with A. homolepis shoots were genetically intermediate, indicating natural hybrids of A. firma and A. homolepis. These 11 hybrids occur in the narrow altitude ranges of their contact zones. The genetic analyses also suggested that hybrid backcrosses with parental species occur. These results support the hybrid hypothesis and suggest that the natural hybrids should taxonomically be classified as A. × umbellata.

中文翻译：

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沿着海拔梯度的冷杉和冷杉的天然杂交和渗入以及对伞形冷杉起源的遗传学认识

日本的温带森林植被带中，有两种冷杉（Pinaceae），冷杉（Abies firma）和A. homolepis。它们的垂直分布完全是隔离的：A. firma发生在低海拔，而A. homolepis发生在升高的区域；他们在大约1,000–1,100 m的高度彼此接触。在接触区周围，伞形按蚊被描述为一棵有高指按插苗的树。它的绿色圆锥体A. FIRMA而不是紫色A. homolepis锥。提出了白化病假说和混合假说来解释伞形线虫的起源，引起了漫长的辩论。因此，我们总共78检查A. firma与和A. homolepis树（包括A.猪苓沿着拔梯度树）中使用13个核微两个研究位点和一个物种特异性叶绿体DNA（叶绿体）标记并检测形貌和圆锥鳞片。最后，我们检验了两个假设。遗传分析表明，A。homolepis和A. firma的枝条形态主要与该物种的遗传特性相对应，而九种具有中间芽形态的树和两棵具有A. homolepis的树（包括伞形树）幼芽基因中间，表明天然杂种A. firma与和A. homolepis。这11种杂种在它们接触区域的狭窄海拔范围内发生。遗传分析还表明与亲本物种发生杂交回交。这些结果支持混合假设和建议，自然杂交应在分类学上被归类为一个。×伞形花序。