Botanical Institute, University of Copenhagen, Gothersgade 140, DK-1123 Copenhagen K, Denmark.
Am J Bot. 2004 Mar;91(3):299-305. doi: 10.3732/ajb.91.3.299.
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.
Orchidantha 的柱头不同于姜目植物的任何其他柱头。它是左右对称的和背腹扁平的，其复杂的结构使植物学家感到困惑，导致了许多不同的描述和解释。在三叶柱头的基部和腹面，可以发现一种专门的“分泌组织”-这里称为黏性组织。当传粉者进入花朵时，来自黏性组织的黏液会涂抹在身体的背面，使其变得粘稠，以便花粉可以附着在上面。黏性组织可能起源于分泌花粉的表皮细胞，在 O. maxillarioides 中，这些细胞和黏性组织之间的形态发生了逐渐变化。然而，在 O. fimbriata 中，没有这样的转变。在 O. fimbriata 的“单向”花朵中，花柱的外围部分由厚壁组织组成，使花柱变硬。然而，在 O. maxillarioides 中，传粉者以相同的方式进出花朵，为了避免自花授粉，当传粉者进入花朵时，柱头被向上推。在这个位置，当传粉者离开花朵时，它无法接触到柱头的接受部分。通过花柱外围部分的厚角组织而不是厚壁组织来实现保持错位位置的花柱的灵活性。
