Biology Reference
In-Depth Information
3.8.13
Euasterids I
In the Euasterid I clade, gynoecial nectaries are common, mostly at the base
of superior ovaries or on top of inferior ones.
Boraginaceae
possesses annu-
lar nectaries at the base of the ovary (Di Fulvio, 1978, 1997; Fahn, 1979;
Cosa de Gastiazoro, 1995; Di Fulvio et al., 1997; Hofmann, 1999). In
Pha-
celia glaberrima
the nectary is located at the base of the tube formed by the
corolla tube and the inner whorl of staminodes, a condition considered ple-
siomorphic for the genus (Cosa de Gastiazoro, 1995). In
Icacinaceae
, most
members seem not to have nectaries, at least according to the absence of the
so-called disc, but it is present in some of them (Cronquist, 1981; Kårehed,
2001), which would indicate receptacular intrastaminal nectaries if the disc
were nectariferous. Anatomical studies showed no nectaries in
Onco-
thecaceae
(Dickinson, 1986b).
Garryales.
Dioecious anemophilous plants characterize this order and con-
sequently, both
Eucommiaceae
and
Garryaceae
have no nectaries
(Cronquist, 1981). It should be noted that in Garryaceae, the intrastaminal
structure present in the staminate flowers is interpreted as a vestigial non-
functional nectary (Liston, 2003).
Gentianales.
There is a wide array of nectaries within this order—mainly
ovarian, but also receptacular, and located on petals or sepals.
Apocynaceae
(Apocynoideae) shows either noteworthy intrastaminal receptacular nectaries
(either surrounding the ovary or as two glands alternating in position with
the two carpels) or has carpellodes transformed into nectaries (Rao & Gan-
guli, 1963; Boiteau & Allorge, 1978; Galetto, 1997; Venter et al., 2001). The
flower and pollination mechanism of Asclepiadoideae is one of the more
complex in angiosperms: flowers have a well-developed staminal and in-
trastaminal corona, anthers and style form a gynostegium, and pollen is
packed in pollinia (Cronquist, 1981). The five nectaries are located inside the
anther wings that also secrete nectar (sometimes called stigmatic chamber),
directly below the entrance of the anther slit, and can be regarded as androe-
cial nectaries; from there, many genera have highly specialized nectar
conducting systems which transfer nectar from the nectaries to secondary
holders formed by the staminal corona (Christ & Schnepf, 1988; Kevan
et al., 1989; Kunze, 1991, 1997). Interestingly, Kevan et al. (1989) demon-
strated that nectar, in addition to being the reward for pollinators, is essential
for the germination of the pollen. The enormous morphological variation of
these structures is of great systematic and phylogenetic importance (Kunze,
1991, 1997). In
Gentianaceae
, although some taxa may not have nectaries,
most genera have nectariferous petals as scales or nectar pits in the adaxial
