Biology Reference
In-Depth Information
it is important to appreciate the constraints that operate on reproductive
characters in that family. Although adaptation to pollinators has played a
major role in floral evolution, sexual selection associated with pollen compe-
tition may have generated conflicting evolutionary pressures acting in
opposition to selection generated by pollinators (Armbruster, 1996).
As nectar is, by far, the most important reward for animal-pollinated
flowering plants (Simpson & Neff, 1983; Proctor et al., 1996), the occurrence,
position, and characteristics of nectaries in flowers are helpful comparative
data for assessing relationships. Owing to the diversity in nectary positions
and structures, floral nectaries are thought to have independently evolved
several times after the angiosperms were already highly diversified, with a
great potential to contribute to the diversification of both plants and animals
(Fahn, 1979; Cronquist, 1988; Lee et al., 2005b). Effectively, fossil records
of insects and angiosperms suggest that the timing of the radiations of some
groups were coincident (Meeuse, 1978; Crepet & Friis, 1987; Crepet et al.,
1991; Pellmyr, 1992).
Despite their biological significance, floral nectaries have been neglected
in plant systematic studies in particular (Chesselet et al., 2002). At the same
time, morphologists have generally not considered nectaries as special struc-
tures and have not paid adequate attention to them (Lorch, 1978). Brown
(1938) attributed the apparent lack of interest in the systematic significance of
nectaries to the fact that as taxonomic studies normally use herbarium speci-
mens they are not always evident in dried plants, as they are small, soft-tissued
structures. Isolated attempts were made at the end of the 19th and the first half
of the 20th centuries (Lorch (1978) and Schmid (1988) give a thorough his-
torical account) to investigate nectaries with a systematic background, e.g.,
Bonnier (1879), Knuth (1906-1909), Brown (1938), Norris (1941), Fahn
(1953), Brown (1961), and Kartashova (1965), among the most relevant. In
later years, Cronquist (1981, 1988) has to be commended for his great interest
in nectaries and the careful effort put into his taxonomical descriptions regard-
ing the presence of nectaries, as well as his attempts to define trends within
families and higher order groups. In parallel, there has been a tremendous in-
terest in reproductive biology, pollination, and breeding system research,
which indirectly includes nectaries. However, in spite of a century of recogni-
tion, and more than two decades of intensive study by systematists and
ecologists, the impact and meaning of reproductive characters as a whole on
systematic treatments is still overlooked or undervalued (Anderson, 1995).
The synthesis of both types of data is sorely needed, because understanding
plant reproductive biology helps to clarify the potential use and value of these
