Dickinson Lab


Comparative morphology: heterotopy and "cruddophytes"

 

Most flowering plants show very regular patterns of relationships between parts: leaves and flowers are inserted on stems, and never the other way around. Well, almost never (Dickinson 1978). In plants like Helwingia japonica (Dickinson & Sattler 1975) flowers always occur on the leaves (below, left). As shown below at the right, this is because the inflorescence primordium that formed originally on the shoot apex (Fig. 12) gets carried up with the growth of the leaf (Fig. 13-15).
Epiphyllous flowers of Helwingia japonica.
Helwingia japonica, male plant at the Arnold Arboretum
with epiphyllous flowers. Photo: T. A. Dickinson.

In other plants, inflorescence primordia may arise on the leaf primordia themselves; this is known as heterotopy, i.e. a change from the usual position of initiation. One such plant is Phyllonoma integerrima (Dickinson & Sattler 1974).

Another example of heterotopy is Phyllobotryon (Flacourtiaceae), with its persistent, multiple epiphyllous inflorescences (far left). A study of inflorescence development in this plant is underway, in collaboration with Dr C. M. Kampny and Dr D. Thomas.

The primordia of fertile Phyllobotryon leaves (near left) bear successive partial inflorescence primordia on their adaxial surfaces.

In this plant the occurrence of leaf-borne inflorescences may be a novel aspect of an unbranched "cruddophyte" habit (below), related to growth on poor soils in the understory of West African tropical rain forests (D. Thomas, personal communication).


The cruddophyte, by C. M. Kampny (detail). © C. M. Kampny 1994.

 

Color photographs and Phyllobotryon micrograph © T. A. Dickinson 1999. Figures 11-15 (Dickinson & Sattler 1975) © Botanical Society of America.


References

T. A. Dickinson. "Epiphylly in Angiosperms." The Botanical Review 44(2): 181-232 (1978).

T. A. Dickinson & R. Sattler. "Development of the epiphyllous inflorescence of Helwingia japonica." American Journal of Botany, 62(9): 962-973 (1975).

T. A. Dickinson & R. Sattler. "Development of the epiphyllous inflorescence of Phyllonoma integerrima (Turcz.) Loes.: implications for comparative morphology." Botanical Journal of the Linnaean Society, 69: 1-13 (1974).


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