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(American Journal of Botany. 2004;91:299-305.)
© 2004 Botanical Society of America, Inc.

Anatomy and Morphology

Anatomy of the unusual stigma in Orchidantha (Lowiaceae)1

Louise B. Pedersen2 and Bo Johansen

Botanical Institute, University of Copenhagen, Gothersgade 140, DK-1123 Copenhagen K, Denmark

The stigma of Orchidantha is unlike any other stigma in the Zingiberales. It is zygomorphic and dorsiventral, and its complicated structure has confused botanists resulting in many different descriptions and interpretations. Basally and ventrally on the three-lobed stigma, a specialized "secretion tissue"—here called the viscidium—is found. When a pollinator enters the flower, mucilage from the viscidium becomes smeared over the dorsal side of the body, making it sticky so that pollen may adhere to it. The viscidium probably originates from secretory pollen-receptive epidermal cells, and in O. maxillarioides a gradual change in morphology between these cells and the viscidium is found. However, in O. fimbriata such a transition is lacking. In the "one-way" flower of O. fimbriata, the peripheral parts of the style consist of sclerenchymatous tissue making the style rigid. In O. maxillarioides, however, the pollinator enters and leaves the flower the same way, and to avoid self-pollination, the stigma is pushed upwards when the pollinator enters the flower. In this position, the pollinator cannot touch the receptive parts of the stigma when it leaves the flower. The flexibility of the style that maintains its dislocated position is accomplished by collenchymatous rather than sclerenchymatous tissue in the peripheral parts of the style.

Key Words: Orchidantha • stigma • viscidium • Zingiberales






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