Patterns of Floral Structure and Orientation in Japonolirion , Narthecium, and Tofieldia

Abstract

Floral evolution requires reassessment in basal monocots, including species formerly assigned to Melanthiaceae, in the light of recent developments in the molecular phylogenetics of monocots. We have investigated flowers of Tofieldia (Tofieldiaceae), Japonolirion (Petrosaviaceae), and Narthecium (Nartheciaceae). We confirm Engler's (1888) hypothesis that orientation of lateral flowers in monocots is dependent on presence and position of additional phyllomes on the pedicel. The type of floral orientation that occurs in Tofieldia is unusual for monocots, since the additional phyllomes are represented by calyculus scales rather than a bracteole, and the outer whorl tepals are initiated alternating with the calyculus scales. In Japonolirion and Narthecium, a bracteole is inserted in an adaxialtransverse or transverse position; either the outer median tepa! is adaxial or no single tepa! is inserted in the median position. In Tofieldia, the pedicel has a calyculus of an abaxial and two adaxialtransverse phyllomes; the outer median tepa! is adaxial. Additional phyllomes on the pedicel are not adaxial, in contrast to adaxial prophylls in the vegetative regions. The presence or absence of a bracteole or calyculus is taxonomically important. Tofieldia pusilla differs from the other species of Tofieldia examined in the absence of a flower-subtending bract, but the calyculus demonstrates some bract-like features in position, structure and development, which can be interpreted as a hybridization of developmental pathways. The abaxial calyculus scale of T. coccinea is delayed in development.

Embryology of Japonolirion (Petrosaviaceae, Petrosaviales): a comparison with other monocots

“…isolated species. J. osense has been studied with respect to floral vascular anatomy (Utech 1984), microspore development (Furness and Rudall 1999), floral structure and orientation (Remizowa et al 2006a), gynoecial morphology and development (Remizowa et al 2006b), and gynoecial anatomy (Rudall 2002). Based on some of these studies, Stevens (2007) summarized the known embryological data as follows: microsporogenesis simultaneous, pollen three-celled, ovules ana-campylotropous, and integumentary obturator present.…”

Harperocallis is congeneric with Isidrogalvia (Tofieldiaceae, Alismatales): Evidence from comparative floral morphology

“…Based on recent molecular phylogenies, Tofieldiaceae are placed in the order Alismatales (APG, 1998;Qiu & al., 2000;Chase & al., , 2006Chase, 2004;Davis & al., 2004;APG III, 2009). Tofieldiaceae are well defined by several synapomorphies, of which the most important is a structure termed a calyculus, which represents three involucral phyllomes surrounding the flower (Takhtajan, 1994(Takhtajan, , 1997(Takhtajan, , 2009Zomlefer, 1997;Remizowa & Sokoloff 2003;Remizowa & al., 2006aRemizowa & al., , 2010aAzuma & Tobe 2010). In all genera of Tofieldiaceae except Harperocallis, flowers are lateral and situated in the axils of well-developed flowersubtending bracts (Takhtajan, 1994(Takhtajan, , 1997(Takhtajan, , 2009Zomlefer, 1997;Remizowa & Sokoloff 2003;Remizowa & al., 2006aRemizowa & al., , 2010a, though a terminal flower is also occasionally present (Remizowa, 2007).…”

Perianth Development in the Basal Monocot Triglochin Maritima (Juncaginaceae)

“…Within Alismatales, Tofieldiaceae (Fig. 1, i) have open, racemose inflorescences with small to medium-sized flowers with a moderately conspicuous or inconspicuous perianth and a calyculus (an annular collar around the pedicel, possibly corresponding to three congenitally fused bracts ;Zomlefer 1997;Remizova and Sokoloff 2003;Remizowa et al 2006). In some species of Tofieldiaceae the calyculus is close to the perianth, similar to a whorl of sepals.…”

“…Typical for this third clade are small, inconspicuous floral units (term including flowers and pseudanthia, definition below) in a dense arrangement, often sessile, sub-sessile, or on a swollen inflorescence axis (spadix) and with a reduced perianth (Eber 1934;Uhl 1947;Hutchinson 1973;Sattler 1965Haynes et al 1998b). The reduction of the perianth in members of clade iii sometimes blurs the distinction between the flower-subtending bract and tepals (e.g., in Apanagetan L. f., Juncaginaceae, some Potamogetonaceae), similar to Acarus L. (Buzgo and Endress 2000) and the calyculus in Tofieldiaceae (Remizova and Sokoloff 2003;Remizowa et al 2006). In contrast, in some other species of Potamogetonaceae, as well as taxa outside this clade with similarly reduced flowers in dense inflorescences (e.g., Araceae), the flowersubtending bract is not included in the perianth, although the bract may be suppressed.…”

“…The concept of the flower-subtending leaf as a marker for an extrafloral position is challenged by studies of some basal monocots (Burger 1977;Buzgo and Endress 2000;Remizova and Sokoloff 2003;Rudall 2003;Remizowa et al 2006) and magnoliids (Tucker 1979(Tucker , 1981(Tucker , 1985Liang andTucker 1989, 1990;Tucker et al 1993;Tucker and Douglas 1996). Some taxa possess reduced flowers that develop unidirectionally (from abaxial to adaxial), in which the first organ of a lateral flower is on the abaxial side of the lateral shoot and could therefore be considered either a flower-subtending bract or a first abaxial tepa!.…”