ABSTRACT Staurastrum gracile is a highly polymorphic species that overlaps morphologically with other species of the genus. The observation of some reproductive features, such as zygospore development, is necessary for correct identification of some Staurastrum species. This study describes the sexual and asexual reproduction of S. gracile in culture and emphasises the importance of characters observed in the fully developed stage of vegetative individuals and zygospores. The description of the life cycle is based on isolated populations from Mexico studied in light and scanning electron microscopy. We describe morphology in the asexual reproductive stages, resulting from an early division before complete cell development, but also results from the number (3, 4, or 7), the length, and the plane of projection of the arms (divergent, moderately divergent to straight, and slightly convergent). We describe gamete fusion type in S. gracile and establish that meiosis occurs in early stages of zygospore formation, characterising the morphology of all stages until germination. The phylogenetic position of the Mexican populations was confirmed by sequence analysis of the ATPase beta-subunit gene (atpB), and the resulting phylogeny was compared with zygospore characters of species. The result suggests that zygospore morphology can be a significant phylogenetic signal in desmid taxonomy.

中文翻译：

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纤细星形藻（Desmidiaceae、Zygnematophyceae）有性和无性生殖阶段的新观察

摘要 Staurastrum gracile 是一种高度多态性的物种，在形态上与该属的其他物种重叠。一些繁殖特征的观察，如接合孢子发育，对于正确识别某些 Staurastrum 物种是必要的。本研究描述了 S. gracile 在文化中的有性和无性繁殖，并强调了在营养个体和接合孢子的完全发育阶段观察到的特征的重要性。对生命周期的描述是基于在光学和扫描电子显微镜下研究的来自墨西哥的孤立种群。我们描述了无性生殖阶段的形态，由细胞完全发育之前的早期分裂产生，但也由臂的数量（3、4 或 7）、长度和投影平面（发散的、适度发散到直线，并略微收敛）。我们描述了 S. gracile 中的配子融合类型，并确定减数分裂发生在接合孢子形成的早期阶段，表征了萌发前所有阶段的形态。墨西哥种群的系统发育位置通过 ATPase β 亚基基因 (atpB) 的序列分析得到证实，并将由此产生的系统发育与物种的接合孢子特征进行比较。结果表明，接合孢子形态可能是硬壳类植物分类学中一个重要的系统发育信号。墨西哥种群的系统发育位置通过 ATPase β 亚基基因 (atpB) 的序列分析得到证实，并将由此产生的系统发育与物种的接合孢子特征进行比较。结果表明，接合孢子形态可能是硬壳类植物分类学中一个重要的系统发育信号。墨西哥种群的系统发育位置通过 ATPase β 亚基基因 (atpB) 的序列分析得到证实，并将由此产生的系统发育与物种的接合孢子特征进行比较。结果表明，接合孢子形态可能是硬壳类植物分类学中一个重要的系统发育信号。