Perianth Development in the Basal Monocot Triglochin Maritima (Juncaginaceae)

Abstract

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 unidirectionally, resulting in an abaxial-median bract-like tepa! and bilaterally symmetrical flowers, similar to those of other basal monocots, such as Aponogeton and Acarus. It is possible that the leaf primordium changes its positional homology from "flower-subtending bract" to "tepa!." 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 APETALAJIDEFICIENS 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.

A developmental study of pollen dyads and notes on floral development inScheuchzeria(Alismatales: Scheuchzeriaceae)

“…The outer whorl abaxial tepal is initiated first and exceeds other tepals in early developmental stages. It is considered that the abaxial tepal of T. maritima incorporates some features of the missing flower-subtending bract (Buzgo et al, 2006;Remizowa et al, 2013).…”

Flowers and inflorescences of the seagrass Posidonia (Posidoniaceae, Alismatales)

“…Here, we present the fi rst detailed description of fl ower anatomy and development in Posidonia , including specimens specifi cally collected by underwater diving several times during a Kaul, 1967a , b ;Sattler, 1972 , 1973 ;Charlton and Ahmed, 1973 ;Sattler and Singh, 1973 ;Leins and Stadler, 1973 ;van Heel, 1988 ;Ronse De Craene and Smets, 1995 ;Charlton, 2004Aponogetonaceae Singh and Sattler, 1977Araceae Lehmann and Sattler, 1992Scribailo and Tomlinson, 1992 ;Barabé, et al, 2000Barabé, et al, , 2002Barabé, et al, , 2011Buzgo, 2001Butomaceae Singh and Sattler, 1974Cymodoceaceae Tomlinson and Posluszny, 1978McConchie et al, 1982Hydrocharitaceae Kaul, 1969Posluszny, 1985 Juncaginaceae Lieu, 1979 ;Charlton, 1981 ;Posluszny et al, 1986 ;Buzgo et al, 2006 ;Remizowa et al, in press Posidoniaceae This study Potamogetonaceae Sattler, 1965 ;Posluszny and Sattler, 1973, 1974a, 1976Posluszny and Tomlinson, 1977 ;Posluszny, 1981 ;Sun et al, 2000 Ruppiaceae Posluszny andSattler, 1974b ;Kaul, 1993 ;Lock et al, 2011 ;Lock, 2012Scheuchzeriaceae Posluszny, 1983 Tofi eldiaceae Remizova and Sokoloff, 2003 ;Remizowa et al, 2005, in press Zo...…”

Open and closed inflorescences: more than simple opposites

“…For example, cotyledon number in Larix is linearly related to the diameter of the apical surface of the embryo (Harrison and Aderkas, 2004). In Alismatales, restricted space availability in the distal portion of the spicate inflorescence seems to explain the adaxial reduction of flower organs, as in Triglochin (Buzgo et al, 2006) and Acorus (Buzgo and Endress, 2000). This view is reinforced by a study concerning different angiosperm families that shows that, at the time of a terminal flower differentiation, IMs form a bulge of a given form, phyllotaxis, and relative size (Bull-Hereñ u, 2010), whereby particularly convex IMs are observed (Fig.…”

“…'closed' inflorescences, represents the ancestral state among species, while the loss of the terminal flower through a process known as 'truncation' has occurred many times in parallel among different angiosperm lineages, giving rise to 'open' inflorescences (Troll, 1964;Stebbins, 1974;Weberling, 1992;Coen and Nugent, 1994;Prenner et al, 2009). While the directionality in the evolutionary change between the closed and the open condition has recently been relativized (Buzgo et al, 2006;Sokoloff et al, 2006;Cavalcanti and Rua, 2008), a second implicit assessment has remained untouched until now, which refers to the uniqueness of the mechanisms by which terminal flowers have been lost (or re-gained) through the evolutionary history of plants. If the truncation of inflorescences always had a common ontogenetic pathway, then every open inflorescence should share a common structure, particularly in respect of the absence of the terminal flower.…”