Continuous petal variation in Epimedium tianmenshanense (Berberidaceae), a species endemic to western Hunan, China

Epimedium tianmenshanense (Berberidaceae), a species endemic to western
Hunan, China, was found to be highly variable in floral characteristics.
In the protologue, its characteristics were described as “flower small,
0.2-0.4 cm diam., inner sepals white, petals as long as inner sepals or a
little shorter than the latter, spur very short, ca. 5.0 mm”. However,
both morphological characteristics and molecular evidence proves that E.
tianmenshanense is closely related to E. baojingense, a taxon with a long
spur.  Based on careful observation in the field and cultivation,
the petals were found to be highly variable in morphology (both shape and
size), being cucullate, subulate, short to long spurred, and with various
transitions. The flowers size varied from small to large accordingly. The
flowers with cucullate and subulate petals, which were a little shorter
than the inner sepals or almost as long as the latter, were small (about
0.8 cm in diameter). The flowers with long spurs, which were much longer
than the inner sepals, were large (about 2.5–3.5 cm in diameter). Finally,
the flowers with short spurs, which were a little longer than the inner
sepals, were medium-sized (about 1.0–1.2 cm in diameter). In addition, the
color of inner sepals was revised from “white, occasionally light
mulberry-purple” to yellowish green or yellowish white. Epimedium
tianmenshanense is a perfect example of natural petal evolution, which
could be used for further taxonomic and evolutionary studies. The reason
for the variation and the taxonomic treatment of the species still need
further study.