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<p>Fern hybrids, a remarkable proportion of which are sterile, provide the basis for hypotheses for species-level divergence between hybrid progenitors using the biological species criterion. Thus, these hybrids can be used to distinguish taxa in complex arrays of understudied and cryptic species. Qualitative morphological features such as anomalies in spore shape, size, and color have often been used to infer sterility as part of identifying fern hybrids. To establish a protocol for quantitative distinction of species and hybrids using spore variation in size and shape, we used spore length and width data originating from an array of 30 genetically profiled specimens of species and 11 of hybrids in the fern genus <i>Polystichum</i>. To assess the possibility of inferring working hypotheses for circumscriptions of species and hybrids using the quantitative data alone, we used a separate set of spore length and width data from a set of 17 type specimens of <i>Polystichum</i>, all without genetic profile. Using the genetically profiled plants, we found that the best quantitative representations of spore variation for distinguishing hybrids from species were coefficients of variation for length and shape (= length/width). These statistics yielded hypotheses for hybrids and species in the type-specimen dataset. The approach developed here is likely to be useful for testing hypotheses for species and hybrids across the ferns, notably in complex arrays including cryptic species, using the biological-species criterion.</p>

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The Biological Species Criterion in Practice: Distinguishing Fern Species from their Sterile Hybrids Using Quantitative Spore Characters

  • 期刊论文

  • 发表日期：

    2026年4月22日

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  • David S. Barrington,
  • Julia E. McClafferty

摘要

Fern hybrids, a remarkable proportion of which are sterile, provide the basis for hypotheses for species-level divergence between hybrid progenitors using the biological species criterion. Thus, these hybrids can be used to distinguish taxa in complex arrays of understudied and cryptic species. Qualitative morphological features such as anomalies in spore shape, size, and color have often been used to infer sterility as part of identifying fern hybrids. To establish a protocol for quantitative distinction of species and hybrids using spore variation in size and shape, we used spore length and width data originating from an array of 30 genetically profiled specimens of species and 11 of hybrids in the fern genus Polystichum. To assess the possibility of inferring working hypotheses for circumscriptions of species and hybrids using the quantitative data alone, we used a separate set of spore length and width data from a set of 17 type specimens of Polystichum, all without genetic profile. Using the genetically profiled plants, we found that the best quantitative representations of spore variation for distinguishing hybrids from species were coefficients of variation for length and shape (= length/width). These statistics yielded hypotheses for hybrids and species in the type-specimen dataset. The approach developed here is likely to be useful for testing hypotheses for species and hybrids across the ferns, notably in complex arrays including cryptic species, using the biological-species criterion.