Winteraceae

Abstract: The Winteraceae are traditionally regarded as the least-specialized descendents of the first flowering plants, based largely on their lack of xylem vessels. Since vessels have been viewed as a key innovation for angiosperm diversification, Winteraceae have been portrayed as declining relicts, limited to wet forest habitats where their tracheid-based wood does not impose a significant hydraulic constraints. In contrast, phylogenetic analyses place Winteraceae among angiosperm clades with vessels, indicating that their vesselless wood is derived rather than primitive, whereas extension of the Winteraceae fossil record into the Early Cretaceous suggests a more complex ecological history than has been deduced from their current distribution. However, the selective regime and ecological events underlying the possible loss of vessels in Winteraceae have remained enigmatic. Here we examine the hypothesis that vessels were lost as an adaptation to freezing-prone environments in Winteraceae by measuring t...

Abstract: The primitive and vesselless angiosperm Zygogynum (Winteraceae), which is restricted to New Caledonia, is pollinated by a moth, Sabatinca (Micropterigidae). Fossil records of both the moth and the plant families extend to the Early Cretaceous. Adult Sabatinca have grinding mandibles and usually feed on the spores of ferns and on pollen. The insects use the flowers as mating sites and eat the pollen which is immersed in a dense pollenkitt. This mode of pollination in which flowers serve as mating and feeding stations with floral odors acting as cues may have been common in the early evolution of flowering plants.

Abstract: Goppert (22) in 1842 noted the absence of vessels in the wood of Drimys Winteri J. R. and G. Forst. His observations have been verified by Eichler (18), Moller (29), De Bary (17), Solereder (34, 35), Strasburger (36), Groppler (25), and many other anatomists and taxonomists. That Trochodcndron has a similar vesselless type of wood was reported by Eichler (18) in 1864. Tetraccntron was subsequently added to the list by Harms (24) in 1897. It was upon the basis of their vesselless wood that van Tieghem (38) segregated the genera Drimys, Pseudowintcra? Bubbia, Belliolum, Exospcrmum, Zygogynum, Trochodcndron, and Tetraccntron in three families of a distinct order, the Homoxylees. Thompson and Bailey (37) and Bailey and Thompson (9) studied all organs and parts of Drimys Winteri J. R. & G. Forst., Pseudowintcra axillaris var. colorata (Raoul) A. C. Sm.. Trochodcndron, and Tetraccntron, and demonstrated that vessels and vessel-like structures are absent throughout both the primary and secondary bodies of these plants. In assembling all available collections of Winteraceae for taxonomic revision, my colleague Dr. Smith (52, 33) has provided me with the unusual opportunity of studying the anatomy of a wide range of accurately identified representatives of the family. Vessels are invariably absent from both the primary and the secondary xylem. Parmentier (30) obviously erred in reporting the presence of vessels in two putative species of Drimys. As van Tieghem (38) and others have shown, Parmentier's observations were based upon incorrectly determined material. Thus, increasing evidence accumulated by many investigators during the last 100 years indicates that the Winteraceae (excluding IUicium), Trochodcndron, and Tetraccntron are the only known living representatives of the dicotyledons that have a primitive vesselless type of secondary xylem. This is not indicative necessarily of close genetic relationship between the Winteraceae, Trochodcndron, and Tetraccntron, as assumed by van Tieghem, but rather the occurrences are to be regarded as retentions of a primitive ranalian type of wood by three families which exhibit diverse trends of specialization in their other vegetative characters and in their reproductive organs. During the last 25 years, the study of the comparative anatomy of the cambium and xylem has progressed rapidly to a stage where it is possible to visualize the salient trends of evolutionary specialization of these tissues