One of the
characteristic of Echinopsis, s.l., is the presence of two
sets of stamens, one an upper series (also called rim or outer
stamens) and the other a lower series (also defined inner or
throat stamens).
There is not a precise technical definitions to
classify the stamens structure in Echinopsis species.
But for a practical use we can utilize a simple terminology:
The upper
series can be named, “rim Stamens”since they
originate on the rim of the throat (but we can alternatively name
them “outer stamens”or “upper stamens”)
The lower
series can be named, “throat stamens” since they
originate within the throat itself.
(also “inner stamens” or “lower
stamens”)
The rim stamens
are arranged in a ring around the throat, their orientation varying
from an erect position to forming a rather flat horizontal spray
against the petals, while the throat stamens take on different
configurations in the different groups.
A
simplified classification of Echinopsis group (Echinopsis, Lobivia,
Pseudolobivia and Trichocereus based on salient flower
morphological configurations.
Lobivia
(Radial symmetrical flowers)
Lobivias show a radial symmetry of
flowers and probably the most primitive stamens arrangment
of Echinopsis, s.l.
In this type of flowers , the rim stamens are all similarly
curved and form a more or less perfect circle, while the throat
stamens form a broad cylindrical wrap completely circling up and
down the throat
Echinopsis, Pseudolobivia
and subg. Trichocereus
(Bilateral symmetrical flowers)
The throat stamens of this plants
undergo a remarkable modification, the rim stamens also becoming
altered, though not as markedly as the throat stamens.
Regarding the throat stamens of these subgenera, those in the
ventral half of the throat have grown in length to form a
prominent exerted (projecting) cluster, the “throat stamen
cluster”, while the throat stamens in the dorsal half (of the
throat tend to decrease in numbers, usually greatly so (Pseudolobivia),
or disappear entirely (subg. Echinopsis and subg. Trichocereus).
An
interesting modification of the filaments of the throat stamen
cluster occurs in subg. Echinopsis and Pseudolobivia. An
extensive basal portion of the filaments in these subgenera have
an adhesive surface that serves to hold the stamens together as
a compact group in the throat. Many throat stamens in subg.
Trichocereus are also held together by the stickiness of their
filaments to form a similar adherent cluster, but other stamens
run courses through the throat independent of the adherent
cluster so that, unlike subg.
Echinopsis and Pseudolobivia, the cluster is not compact in the
throat, but appears as a broad, loose assemblage of stamens.
The flower tube of bilaterally
symmetrical flowers is sometimes also modified: Its ventral side
is slightly longer than the dorsal side, so that the surface of
the flower is slightly inclined.
The rim stamens in the three subgenera also show bilateral
symmetry: Looking at a flower from a top view, the rim stamens
on the ventral half of the flower tend to be hook-shaped while
those on the dorsal half are merely weakly curved. As a result,
when the rim stamens are arranged in a horizontal spray over the
petals, they do not form a perfect circle, as in radially
symmetrical flowers, but a circle that is somewhat flattened on
its ventral side.
Bilateral symmetry is part of the pollination syndrome
(strategies for attracting particular kinds of pollinators) and
serves to attract a different class of pollinators than those of
radially symmetrical flowers.
Bibliography:
ECHINOPSIS REVISITED, April 28, 2004. By Bob Schick
