in the positions of the other sepals. In addition, partial petal
conversion was observed in BPP flowers, with typical tissues of
both sepals and petals being evident on the same structure (Fig. 2c
and d, arrows). Petal to sepal conversions always occurred
underneath the enlarged phylloid structure at a position at which
the first petal would be expected.
In young flower buds, the distinctive enlarged sepal beneath the
calyx was already apparent before the actual bending of the stem.
Therefore, the presence of a lower enlarged sepal was used as an
early-stage indicator of BPP.
An examination of the enlarged phylloid structure in BPP
showed large variations both in positions along the stem – from
directly flanking the flower bud to few centimetres beneath it –
and in shape – from sepalloid to leaf-like (Fig. 3a). The number of
leaflets on the phylloid structure also varied considerably from
stem to stem. No axillary bud was present in the axil of the phylloid
structure (Fig. 3b and c), supporting the sepal origin of this
structure. Yet, sections of the phylloid showed the presence of
palisade parenchyma cells (Fig. 3f), which are characteristic of
leaves (Fig. 3d) but are absent from sepals (Fig. 3e). Taken together,
these findings suggest that the phylloid represents a transformation
of the first sepal into a leaf-like entity.