Abstract Detail



Anatomy and Morphology

Stevenson, Dennis [1].

Leaf and leaflet morphology in the Cycadales.

The terms spine, prickle, and thorn have been variously used interchangeably in plant descriptions and cycads are no exception.  It is clear from developmental studies and morphology that cycads do not have thorns but rather spines and prickles.  Spines are present as reduced leaflets in species of Cycas, Dioon, Encephalartos, and Macrozamia, and none of these genera have prickles.  In contrast, some species of Zamia and Ceratozamia have prickles, but none have spines.  Lepidozamia, Bowenia, and Stangeria have neither. Another leaf form is cataphylls as reduced leaves.  However, Stangeria has no cataphylls but rather an adaxial hood-like structure at the base of the petiole that remains on the stem after abscission and functioning as a cataphyll. Bowenia has cataphylls only on reproductive axes.  Zamia and Ceratozamia have small stipules on both cataphylls and leaves. Most cycads have pinnately compound leaves except for Bowenia and some species of Macrozamia, which have bipinnate leaves. Some species of Cycas have leaflets that are pentapinnate or more.  In Cycas, the leaves are imparipinnate in contrast to the other genera that are paripinnate except in the seedling stages. That terminal leaflet is represented as a undeveloped rudiment. Leaflet initiation appears to be basipetal on the leaf primordium.  Although this would seem to be inconsistent with mature morphology that indicates an acropetal series, it appears that maturation pattern is the reverse of the initiation pattern.


Related Links:
Cycad Pages
World List Of Cycads


1 - New York Botanical Garden, 2900 Southern Blvd, Bronx, NY, 10458, United States

Keywords:
cycads
spines
prickles
cataphylls
stipules.

Presentation Type: Oral Paper
Number: 0005
Abstract ID:289
Candidate for Awards:None


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