Searching for diamonds in the apomictic rough: a case study involving Boechera lignifera (Brassicaceae)

The genus Boechera is one of the most difficult species complexes in North America, with about 70 sexual diploids and hundreds of apomictic taxa representing diverse combinations of nearly every known sexual genome. In this study, we set out to clarify the taxonomy of Boechera lignifera, which currently includes a small number of sexual diploid populations in addition to the widespread apomictic diploid upon which the name is based. Using data from cytological studies, microsatellite DNA analyses, geography, and morphology, we demonstrate that the apomictic populations are genetically quite divergent from the sexual diploids. We propose the name Boechera kelseyana to accommodate the sexual diploid taxon, which occurs entirely south of the geographic range of B. lignifera. Boechera kelseyana is consistently separable from B. lignifera based on pollen and seed morphology, the length and proximal orientation of fruiting pedicels, differences in the branching and orientation of trichomes on the lowers stems, and the number of flowers and cauline leaves on unbranched fertile stems.

弯蕊芥属（Boechera）是北美地区最棘手的物种复合群之一，该类群包含约70个有性二倍体类群，以及数百个无融合生殖类群，这些无融合生殖类群几乎涵盖了所有已知有性基因组的多样组合。本研究旨在厘清林生弯蕊芥（Boechera lignifera）的分类学问题，当前该类群除了以其命名的广布无融合生殖二倍体外，还包含少量有性二倍体种群。本研究利用细胞学研究、微卫星DNA分析、地理分布数据以及形态学数据，证明无融合生殖种群与有性二倍体种群在遗传上存在显著分化。我们提议将该有性二倍体类群命名为凯尔西弯蕊芥（Boechera kelseyana），该类群的分布范围完全位于林生弯蕊芥（B. lignifera）分布区以南。凯尔西弯蕊芥（Boechera kelseyana）可通过以下特征与林生弯蕊芥（B. lignifera）稳定区分：花粉与种子形态、果梗的长度与近轴朝向、下部茎的毛状体分枝与朝向差异，以及不分枝可育茎上的花朵数和茎生叶数量。