Hesperoyucca Whipplei - Taxonomy

Taxonomy

The taxonomy of Hesperoyucca whipplei is complex and controversial. Hesperoyucca was described as a genus by Georg Engelmann as long ago as 1892, but it has taken recent DNA analysis to confirm that they are genetically distinct from Yucca. The splitting of Hesperoyucca from Yucca is still not widely reflected in available literature or online (for example, the British Royal Botanic Gardens, Kew and the Royal Horticultural Society websites do not recognise the name as current).

Among those botanists who have treated (or still treat) it as a species of Yucca, six subspecies have been recognised (Hochstätter 2000, 2002, 2004); others have regarded them as varieties. Yet others (e.g. Flora of North America and the Jepson Flora) do not recognise any subspecies or varieties (within either Yucca whipplei or Hesperoyucca whipplei ), as the wide variability within the species precludes the segregation of discrete subspecies.

Hochstätter's subspecies are:

• Yucca whipplei ssp. whipplei
• Yucca whipplei ssp. caespitosa
• Yucca whipplei ssp. intermedia
• Yucca whipplei ssp. percursa
• Yucca whipplei ssp. newberryi
• Yucca whipplei ssp. eremica

The plant treated as the subspecies Yucca whipplei subsp. newberryi has been shown to be genetically distinct, and is often treated as a distinct species, Hesperoyucca newberryi. It is native further east, in Arizona, and differs in the capsules being unwinged or with only slight wings.