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Two species are recognized within the genus,H. monogyra Torr. & Grayex Gray andH. salsola Torr. & Grayex Gray. Of these, the fall-floweringH. monogyra is monomorphic and unambiguous. The springfloweringH. salsola, however, is polymorphic and contains elements that have often been segregated as distinct species. Examination of character intergradation and interpretation of morphological variation against the evolution and distributional backgrounds indicate that the latter complex is best treated within three varietal taxa:H. salsola var.fasciculata, with wings of the fruiting involucres appressed and spirally arranged;H. salsola var.salsola, with wings emergent and spirally arranged; andH. salsola var.pentalepis, with wings strongly emergent and whorled. |
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