The Gynoecium of Engelhardia Spicata (Juglandaceae) ant its Phylogenetic Significance
Acta botanica neerlandica , Volume 13 - Issue 3 p. 352- 366
1. After a concise survey of a neomorphological approach of the evolution of the one-ovuled gynoecia of several angiospermous groups the homology of certain pistils with one-ovuled pteridospermous cupules is postulated. 2. The morphology of the pistil of Engelhardia spicata is discussed in terms of this new interpretation, and seen in this light the so-called “female flowers” of the Juglandaceae may be expected to consist of a bitegmic ovule enveloped by the homologue of the cupule (the gnetalean “chlamys”). 3. The close semophyletic relationship between the juglandaceous “female flowers” and the chlamydote ovules (one-ovuled cupules) of the gnetalean Cycadopsids is strongly suggested by the presence of a distal extension of the inner integument in E. spicata which is manifestly the homologue of the micropylar tube or tubillus of chlamydospermous forms, so that apparently in all Juglandaceae the outer integument must be represented by the “ovary wall” (conventionally of carpellary derivation), and the cupule by the third covering (traditionally the “perianth” or “calyx”) which is partially adnate to the second integument. 4. The gynoecia of Engelhardia and of several, or all, other genera of the Juglandaceae are technically still “gymnospermous”, their primary micropyles being exposed, and they provide a series of transitional stages between the primitive gnetalean condition and an almost complete state of “angiospermy” by showing the gradual coalescence of the distal regions of the integuments and the cupule homologue. 5. The advent of “angiospermy” or, probably more correctly, pseudoangiospermy in the Juglandales initiated as the lateral adnation of the distal region of the outer integument to the terminal portion of the micropylar tube of the inner integument (the exostomium formed by the tubillus remaining exposed), conceivably after the differentiation of the distal end of the tubillus into an infundibuliform stigmatic area, followed by the severance of the connection between the perinucellar portion of the integument and its narrow tubular extension (».«., the stylar canal or conductive stylar tissue in a more conventional terminology) that coalesced with the outer integument by the reduction of the proximal part of the integumentary tube. 6. A singular characteristic of the Juglandales, viz., the presence of a cavity (“ovary chamber”) between the outer and the inner integument is associated with the formation of parenchymatous tissue and of “false” partitions between the integuments: the intertegumentary “packing (or filling) tissue” most probably originated as a lateral rim-like extension of the basal portion of the tubillus as found in some gnetalean forms, and during the evolution of the pistil subsequently proliferated basipetally. 7. In other angiospermous forms the lateral and basipetal outgrowths of the collar of the micropylar tube became extended peripherically (over the outside) of the outer integument, so that the angiospermy or pseudo-angiospermy in these taxa can only have been attained by a coalescence of the cupule homologue (chlamys) with the micropylar region of the tubillus without the participation of the outer integument in the formation of the “stylar” and “stigmatic” area of the “pistil”; derivatives and remnants of basipetally developed outgrowths of the micropylar tube overarching the outer integument are frequently met with in the form of arillodes, obturators and caruncles. 8. Not only has the fundamental significance of the gynoecial morphology of E. spicata in the reconstruction of the evolutionary history of the Angiosperms thus been demonstrated, but the structure of the juglandaceous pistil is also particularly instructive in showing at least two alternative ways of the gradual change-over from “gymnospermy” to “angiospermy” leading to primarily oneovuled pistils which are perhaps only pseudo-angiospermous in that the exostomium of the original micropyle, i.e., the distal end of the “stylar canal” (a derivative of the tubillus!), is still exposed.
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A.D.J. Meeuse, & J. Houthuesen. (1964). The Gynoecium of Engelhardia Spicata (Juglandaceae) ant its Phylogenetic Significance. Acta botanica neerlandica, 13(3), 352–366.
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