Annals of Botany

Floral morphology and anatomy of Ophiocaryon, a paedomorphic genus of Sabiaceae

Ophiocaryon is a lesser-known genus in Sabiaceae, hitherto without detailed floral study and with unknown pollination mechanisms. Thaowetsuwan et al. examined floral morphology and anatomy revealing several unusual characters:

  • conical cells on petals
  • different kinds of orbicules in anthers
  • stomata on nectary appendage tips and ovary
  • two distinct surface patterns on stamens and ovary
  • tanniferous cell layers in the ovary wall
  • acorn-shaped unitegmic ovules with very short integuments
Inflorescence and mature flowers of a representative species of Ophiocaryon
Inflorescence and mature flowers of a representative species of Ophiocaryon (O. heterophyllum). (A) Compound leaves and inflorescence. (B) Partial inflorescence with blooming flowers. (C) Mature flower close to anthesis. Note that the two inner petals are smaller than the three outer petals (arrowheads point to smaller petals). (D) Mature flower at anthesis. Scale bars: (A) = 1 cm; (B–D) = 500 μm. Source: Thaowetsuwan et al. (2017)

Comparative study between Ophiocaryon and Meliosma, its sister genus, found that the calyx, corolla, androecium and gynoecium of Ophiocaryon resemble an undeveloped state of the latter taxon, reflecting a paedomorphic regression of the flower of Ophiocaryon. However, no synapomorphies were found between Ophiocaryon and M. alba, its closest sister group. Moreover, the findings of scent, presence of conical cells on petals and a nectary suggest flowers are pollinated by small insects with a secondary pollen presentation on the cupula of fertile stamens.

However, the comparative timing of development between Meliosma and Ophiocaryon cannot be obtained from the results of this study; therefore, the authors cannot estimate whether progenesis or neoteny is responsible for the occurrence of paedomorphosis in Ophiocaryon.

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