Biology Reference
In-Depth Information
On the other hand, nectaries may have a different organization: either
unilaterally located in the flower, having an irregular shape (usually with a
part larger than the rest), and being a component of a spur (e.g., in Balsami-
naceae, Lentibulariaceae, and Orchidaceae). Therefore, they have only one
plane of symmetry and are thus bilaterally symmetrical, although in the lit-
erature they have been referred to, inappropriately, as asymmetrical (e.g.,
Zer & Fahn, 1992; Galetto, 1995b; Petanidou et al., 2000). Concerning the
unilaterally organized nectaries (Fig. 3B), the receptacular nectaries in some
species of Lythraceae, Melianthaceae, and Sapindaceae, and the ovarian nec-
taries in a number of Goodeniaceae, Lamiaceae, Gesneriaceae, Scrophu-
lariaceae, Pedaliaceae, Phrymaceae, and Plantaginaceae (mainly the former
Globulariaceae) can be mentioned (e.g., Cronquist, 1981; Dafni et al., 1988;
Leins & Erbar, 1989; Zer & Fahn, 1992; Galetto, 1995b; Petanidou et al.,
2000; Decraene et al., 2001; Nepi et al., 2003; Ilhenfeld, 2004b). In some
cases, e.g., in Lamiaceae and Scrophulariaceae, radially and bilaterally
symmetrical nectaries have been found in different genera of the family, but
more data at the specific and generic levels are needed to assess their sys-
tematic significance.
3.1.5
Number
Within a flower, nectaries can be differentiated as a single structure of nec-
tariferous tissue (e.g., annular rings on the receptacle or at the base of the
ovary), or as a number of individual glands (e.g., cushions on each petal base
or several glands on the receptacle), whose shape and size may be equivalent
or dissimilar. All these traits may have taxonomic value and have to be con-
sidered when studying a particular plant group. For instance, in Brassicaceae
(Norris, 1941; Deng & Hu, 1995; Davis et al., 1996, 1998, 1999), nectaries
can be annular, or composed of a number of individual glands (two, four, or
eight), depending on the genus. On the other hand, SanMartin-Gajardo and
Sazima (2005) reported that in Gesneriaceae the number of nectaries per
flower not only shows interspecific variation, but also intraspecific variation
(e.g., mostly five glands or two fused plus three in
Vanhouttea
, or one, two,
or four glands in
Sinningia
).
In 1998, Davis et al. proposed the resurrection of the term
nectarium
(coined by Linnaeus, 1735) to represent collectively the multiple nectaries
that can be found in individual flowers. This proposal for the Brassicaceae, a
family with a ring of nectariferous tissue, or two, four, or eight individual
nectaries that may be interconnected (Davis et al., 1996, 1998), may well be
applicable to any flowering plant. Thus, nectarium would represent all sepa-
rated nectaries of a flower abstractly (whether the mentioned connections
