Biology Reference
In-Depth Information
Asteraceae (Wist & Davis, 2006), Bignoniaceae (Galetto, 1995a), Boragina-
ceae (Weryszko-Chmielewska, 2003), Brassicaceae (Davis et al., 1998),
Campanulaceae (Galetto et al., 1993), Caryophyllales (Zandonella, 1977),
Convolvulaceae (Galetto & Bernardello, 2004), Crassulaceae (Said, 1982),
Cucurbitaceae (Nepi et al., 1996), Ericaceae (Palser et al., 1991), Euphor-
biaceae (Freitas et al., 2001), Fabaceae (Davis & Gunning, 1991),
Gesneriaceae (Maldonado & Otegui, 1997), Hydroleaceae (Di Fulvio, 1997),
Lamiaceae (Dafni et al., 1988), Loranthaceae (Galetto et al., 1990), Melian-
thaceae (Decraene & Smets, 1999a; Decraene et al., 2001), Myrtaceae
(Davis, 1997), Plantaginaceae (Nepi et al., 2003), Rosaceae (Radice & Galati,
2003), Rubiaceae (Galetto, 1998), Solanaceae (Rodriguez, 2000), and Tro-
paeolaceae (Fabbri & Valla, 1998), among many other families.
According to Endress (1995), modified stomata are apparently absent
from monocotyledons. In these plants, nectar is secreted by trichomes or by
diffusion through the epidermis. Alternatively, nectar is mainly collected in
inner cavities of septal nectaries and is released to the outside through spe-
cial slits. Recently, Davies et al. (2005) reported the existence of stomata in
the labellum of an orchid, a finding that may imply that stomata may be pre-
sent in other orchids as well, but data are needed to support this assertion.
Both the number and location of stomata on nectaries may differ among
closely related species. Although available data are scarce, this feature may
have taxonomic importance and should be considered more carefully (e.g.,
Palser et al., 1991; Galetto, 1995a, 1997, 1998; Petanidou et al., 2000; Rod-
riguez, 2000; Weryszko-Chmielewska et al., 2003; Galetto & Bernardello,
2004). In addition, occasionally the distribution of stomata may be restricted
to specific parts of the nectary, forming a single group or multiple fields of
stomata (e.g., Davis & Gunning, 1992; Galetto, 1995b; Vogel, 1998c). The
significance of these features in plant systematics is mostly unexplored, al-
though the diversity of stoma fields was regarded by Vogel (1998c) as a
promising criterion.
In relation to the epidermis, the position of stomata may be sunken, iso-
bathic, or elevated. Data on several Lamiaceae species showed that this
position was affected by growing conditions (Petanidou et al., 2000); there-
fore, the alignment of stomata on the nectary surface cannot be considered a
reliable taxonomic character, at least according to this evidence.
Parenchyma.
Turning to the modifications of the specialized parenchyma of
the nectary, the main differences include being either uni- or multilayered,
and presenting chloroplasts (Vassilyev & Koteyeva, 2004a), amyloplasts
(Nepi et al., 1996), or both (Maldonado & Otegui, 1997). The presence and
