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Throat stamen  [ Botany  ]
(Echinopsis flower morphology)

Dictionary of botanic terminology - index of names

Synonyms: Inner stamens, Lower stamens
  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.
(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.

ECHINOPSIS REVISITED, April 28, 2004. By Bob Schick







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