Exploratory hybridization of red alder (Alnus rubra Bong.) and white alder (Alnus rhombifolia Nutt.) was conducted to initiate a long-term investigation into the inter-specific taxon’s potential for biomass production. Red alder selections originated in stands west of Oregon’s Cascade Mountains, while white alder came from provenances west and east of the Cascades. White alder’s heretofore unknown chromosome number was determined equal to red alder (2n = 2x = 28) and included a pair of satellite chromosomes. An experimental crossing technique was proven, establishing the species’ reproductive affinity for the first time. Hybridization was substantially more productive when red alder served as the female parent as opposed to white alder. Hybridity was confirmed using four species-specific SSR markers developed from transcriptome resources for identifying sib relationships in domesticated populations. To begin a description of the inter-specific taxon, hybrids and their open-pollinated siblings were assessed at ages four through six for morphological and phenological traits and carbon and nitrogen isotopic ratios in a field planting in western Washington, USA. Principal component analysis of quantitative leaf and internode morphologies showed that red alder and hybrid alder are relatively comparable and both are distinct from white alder. Qualitative differences in leaf morphology are more diagnostic with inter-specific hybrids often intermediate to red and white alder. Principal coordinate analysis of molecular data cleanly separated the three taxa. Plans for continued investigation of the taxon as a biomass crop species are discussed including a potential role for inter-specific hybrids in adapting red alder to the effects of climate change.

对红色al木（Alnus rubra Bong。）和白色al木（Alnus rhombifolia Nutt。）进行了探索性杂交，以长期研究种间分类群在生物质生产方面的潜力。红al木的选择起源于俄勒冈州喀斯喀特山脉以西的林地，而白der木则来自喀斯喀特山脉以西和东部的物源。确定白al迄今未知的染色体数等于红red（2 n  = 2 x = 28），并包括一对卫星染色体。证明了一种实验性杂交技术，首次建立了该物种的繁殖亲和力。当红色al木充当雌性亲本时，与白色al木相反，杂交实质上更具生产力。使用从转录组资源中开发出的四个物种特异性SSR标记来确认杂种，以鉴定驯养种群中的同胞关系。为了开始描述种间分类单元，在美国华盛顿州西部的田间种植中，对4至6岁的杂种及其开放授粉的同胞进行了形态和物候特性以及碳和氮同位素比的评估。定量叶片和节间形态的主成分分析表明，红色al木和杂种al木具有相对的可比性，并且都不同于白色distinct木。叶片形态的质性差异可以通过种间杂种进行诊断，这些种间杂种通常介于红der木和白der木之间。分子数据的主坐标分析将三个分类单元完全分开。讨论了继续研究分类单元作为生物量作物物种的计划，其中包括种间杂种在使红der木适应气候变化影响方面的潜在作用。