Sectile pollinia and relationships in theOrchidaceae

Abstract

Abstract:The sectile state, in which pollinia are subdivided into units larger than tetrads, is one of several systematically important orchid pollinium characters. We recognize two types of sectile pollinia, based upon form and arrangement of massulae. One type is found primarily in members of Orchidoideae-Spiranthoideae, while the other characterizes epidendroid genera. Additional characters that have systematic potential are massula dimorphism, caudicle composition, and degree of tetrad packing. Hollow sectile pollinia unite Arethusa and CaIopogon; Stereosandra and Epipogium have dissimilar pollina, but other characters support a close relationship between them. The sectile condition is interpreted as resulting from a shift in the timing of cohesion of developing pollen cells.

Mechanism of Spontaneous Autogamy in the Allogamous Lepidopteran Orchid Gymnadenia Conopsea (L.) R. Br. (Orchidaceae)

“…The anther contains two parallel chambers covered by thin-walled, attenuated and partially free anther thecae at the base, which open by a slit (Szlachetko and Rutkowski, 2000;Box et al, 2008). Each chamber contains one pollinarium with a clearly distinguishable sectile pollinium (formed by the pollen tetrads, bound together by elastic threads in the massulae) and a long caudicle, which is attached to a sticky viscidium (Darwin, 1877;Freudenstein and Rasmussen, 1997;Claessens and Kleynen, 2011). Caudiculae exhibit the ability of a bending movement when the viscidium adheres to a pollinator's proboscis which brings the pollinia into the appropriate position for touching the stigma (Darwin, 1877).…”

Impact of floral traits on the reproductive success of epiphytic and terrestrial tropical orchids

“…Nectar presence was detected in the Weld by using a hand lens or by examining spurs under a scanning electron microscope. The types of pollen dispersal units in orchids are complex (Pacini and Hesse 2002), but we distinguish here only between those pollinia which can break up following dispersal, termed "sectile" by Freudenstein and Rasmussen (1997), from those which cannot (termed "non-sectile"). The number of pollinia of each species and their type were recorded in the Weld by using a hand lens or in the laboratory under a microscope.…”

Understanding the Phylomorphological Implications of Pollinia from <i>Dendrobium</i> (Orchidaceae)

“…Earlier, the anatomy and development of orchid pollinia have received careful study with both SEM and tissue the sections with significant contributions on epidendroids by [18,34,35]; [14], and reviewed by [28]. Moreover, across orchid taxa, the pollinium had shown apparent evolutionary signatures, those may be important for pollen delivery and also for modulating the adhesion, hydration, and emergence of pollen tubes [36].…”

“…These variations in pollen grains are also reported to be related to the evolved pollination strategies, however, with enormous interspecific variability. Pollen characters have frequently been observed to assess structural diversity [2,3], and also for their usefulness defining evolutionary trends in plant families such as Araceae [6], Callitrichaceae [7,8], Hydrocharitaceae [9], Fabaceae [10], Scrophulariaceae [11], and Orchidaceae [12][13][14].…”

“…Among flowering plants, the family Orchidaceae is the largest with more than 2500 reported species [13,15], and is known for its enormous diversity in pollen morphology [14]. The diversity has been observed at different levels: variability in packing of pollen in pollinia, in pollen wall structure, and in pollen surface sculpturing [16].…”