I'm thinking this is becoming somewhat confused, as orchids belong to the monocots, therefore many orchids demonstrate a somewhat characteristic lack of a leaf petiole, instead being attached directly to the stem of the plant. Monopodial orchid leaves very often have what is termed a sheath (just like the protective sheath typically seen in a Cattleya and other orchid flower inflorescences) as part of the leaf, and which attaches to the stem, but this is different from a petiole, which is a typically slender projection from the stem which at its end bears a leaf, or leaflets. When a single leaf grasps the stem of the plant directly, generally encircling the stem, and lacks a petiole, it is classified as sessile and not petiolate.
Leaves have an abscission zone, most often containing a differentiated abscission layer but sometimes this layer is lacking, where dying and dead leaves loosen and fall from the plant. When the abscission layer is lacking the leaf simply remains on the plant until it rots away. Orchids can be in either of these groups.
Stanhopea would be one typical example of an orchid genus whose members often bear a leaf petiole.
Last edited by Hiester; 06-15-2014 at 08:57 PM..
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What happened to my petiole.
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