Putative lycopsids

There are always fossils that remain impossible to place systematically. The enigmatic Devonian-Carboniferous plant Barinophyton is one of these. Members of the genus consist of alternately arranged naked branches with sporangia organized in two rows on laterally born (FIGS 9.122, 9.123), spikelike fructifications. Structurally preserved specimens of B. citrulliforme from the Devonian of New York include an exarch protostele (Brauer, 1980). The tracheids have a continuous secondary wall that is plicated into the cell lumen, simulating annular secondary wall thickenings. Between the plications, the wall contains numerous delicate pits, each with a recognizable border. The sporangiferous appendages are alternate and two-ranked; each appendage is recurved and bears one large sporangium on the concave surface within the curve. An unusual feature of Barinophyton is that several thousand microspores and ~30 megaspores

Barinophyton
figure 9.122 Suggested reconstruction of Barinophyton citrulliforme showing two rows of sporangia in a strobilus-like organization. (From Kenrick and Crane, 1997a.)

occur together in the same sporangium. A similar condition exists in Protobarinophyton pennsylvanicum described from the Upper Devonian of New York (Brauer, 1981). The small spores range from 30-42 pm in diameter, whereas the large spores extend from 410 to 560 pm. In both Barinophyton (Taylor and Brauer, 1983) and Protobarinophyton (Cichan et al., 1984) the wall structure of the large and small spores is different. This indicates that the small spores do not merely represent aborted megaspores and that these two plants were, in fact, heterosporous. Spores of two different sizes have also been reported in the same sporangium of the progym-nosperm, Archaeopteris (Medyanik, 1982) (Chapter 12). In A. latifolia the number of megaspores per sporangium is highly variable, ranging 8-20 (Chaloner and Pettitt, 1987).

figure 9.123 Portion of Barinophyton citrulliforme axis with appendages (A) and sporangia (S) (Devonian). Bar = 1.5 cm. (Courtesy D. F. Brauer.)

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