Biology Reference
In-Depth Information
knowledge of their evolution, a principle that always has to be borne in mind
(Smets et al., 2000).
In Fig. 7, the main nectary types in each clade recognized by APG II
(2003) are mapped to follow their fate, summarizing the information given in
the previous section, where the appropriate references are cited.
In the early-branching lineages, nectaries are rare, which would indicate
that this condition is plesiomorphic. Amborellaceae, the sister group for the
flowering plants, has no nectaries, as also happens in Austrobaileyales and
Chloranthaceae, and Nymphaeaceae has only simple petal nectaries. In
Magnoliids, nectaries are present mainly as sepal (Piperales), petal (Magno-
liales), or staminal (Magnoliales, Laurales) nectaries. Stigmatic exudates are
also frequent in several families from these lineages—Annonaceae, Austro-
baileyaceae, Chloranthaceae, Magnoliaceae, Monimiaceae, Winteraceae—
thus forming an alternative reward for the group; nevertheless, their bio-
logical significance has to be examined to be sure of their role in the
reproduction of the taxa involved.
In monocots as a whole, septal nectaries are characteristic since they are
widely distributed and are exclusive to this lineage, although some species-
rich groups (such as Liliales and Orchidaceae) lack them entirely. Acorales,
the sister group of all monocots, has no nectaries, which would again be the
plesiomorphic condition. In Alismatales, the basal Araceae also has no nec-
taries, as happens in other families as well, but septal nectaries are frequent
in many others. In Asparagales (except for Orchidaceae and Hypoxidaceae)
and Dioscoreales septal nectaries are widespread, but they are completely
absent in Liliales (where tepal nectaries are the rule). Most families of Pan-
danales are nectarless; only Velloziaceae is reported to have the typical septal
nectaries. In Commelinids, septal nectaries are present in Dasypogonaceae, in
some Arecales, only in Bromeliaceae within Poales, in most Commelinales,
and in the majority of Zingiberales. Other nectary types also found in several
lineages are tepal and staminal, but at a lower frequency.
Ceratophyllales, the sister group of the Eudicots and Core Eudicots, has
no nectaries, again probably a plesiomorphy. In Eudicots, petal nectaries are
widespread, being characteristic of the basal Ranunculales. In addition, in-
trastaminal receptacular, staminal, and gynoecial (not ovarian) nectaries are
less frequent. In Core Eudicots, intrastaminal receptacular nectaries (con-
tinuous or fragmented) are common, probably representing the basal
condition, followed by sepal, petal, and gynoecial nectaries. In Rosids, both
intra- and extrastaminal nectaries are widespread, after ovarian, hypanthial,
