Basal monocots exhibit considerable variation in inflorescence and floral structure. In some cases,

such as Triglochin maritima, it is not clear whether the lateral and terminal structures of the inflorescence

are flowers or pseudanthia, or where the limits between flowers and inflorescence lie. To address

these questions, morphological studies were carried out, and the results show that in T. maritima both

terminal and lateral structures are flowers, not pseudanthia. The terminal flower of T. maritima develops

from the apical inflorescence meristem, suggesting that the apical meristem identity changes

from ‘‘inflorescence'' to ‘‘flower'' during inflorescence development. In addition, distal flowers of T.

maritima are reduced, and there is no distinct flower-subtending bract; instead, the perianth develops

are reduced, and there is no distinct flower-subtending bract; instead, the perianth develops

unidirectionally, resulting in an abaxial-median bract-like tepal and bilaterally symmetrical flowers,

similar to those of other basal monocots, such as Aponogeton and Acorus. It is possible that the leaf

primordium changes its positional homology from ‘‘flower-subtending bract'' to ‘‘tepal.'' Therefore,

in some basal angiosperms with abbreviated development of lateral flowers the demarcation of the

flower vs. the inflorescence is ontogenetically ambiguous. In situ hybridization experiments show that

a putative ortholog of the B-class gene APETALA3/DEFICIENS is expressed in developing stamens

and carpels, and may also be expressed in the shoot axis of the very young inflorescence. This

expression pattern seems to be consistent with the gradual transition between inflorescence and flower

that was observed morphologically.