Pentaphragma: A Unique Wood and its Significance

Qualitative and quantitative data are given for wood anatomy of three species of Pentaphragma (Pentaphragmataceae); the woods of the three species are very similar. Pentaphragma is rayless, but eventually develops rays in at least one of the species studied. This is interpreted as related to secondary woodiness or upright habit within a predominantly herbaceous phylad. The vessel elements of Pentaphragma have features universally interpreted as primitive in dicotyledons: scalariform perforation plates with numerous bars; pit membrane remnants in perforations; scalariform lateral wall pitting; the genus also has fiber-tracheids with prominently bordered pits. These character states accord with the basal position in Campanulales accorded Pentaphragmataceae by Cosner et al. (1992), and suggests that order may have begun with more numerous primitive features than generally recognized. The presence of occasional scalariform perforation plates, often aberrant, in secondary xylem of families of Asterales sensu lato - Campanulaceae, Pentaphragmataceae, Valerianaceae, and even Asteraceae (e.g., certain Lactuceae) - can be attributed to paedomorphosis, extending these plates into secondary xylem from primary xylem. Raylessness in Pentaphragma can be described in terms of secondary woodiness or paedomorphosis. The fact that fiber-tracheids are shorter than vessel elements in Pentaphragma is believed related to raylessness also, because some fiber-tracheids are produced from 'potential' ray areas.

Wood Anatomy and Stem of Chloranthus; Summary of Wood Anatomy of Chloranthaceae, with Comments on Relationships, Vessellessness, and The Origin of Monocotyledons

In contrast to the monopodial Ascarina and Hedyosmwn, Chloranthus and Sarcandra are sympodial. Sarcandra and C. erectus have woody canes of finite duration, whereas other species of Chloranthus have shoots of one year's duration ; these latter species have second year wood only on rhizome s, not on upright shoots. Rhizome portions transitional to upright sterns were selected for study. Chloranthus erectus has abundant septate fibretracheids, C. japonicus none, and two other species a few. Chloranthus (and Sarcandra) have rays of two distinct sizes in wood: rays that are extensions of primary rays, and uniseriate and biseriate rays in fascicular areas . Wood anatomy of each of the four genera can be characterised, and is summarised in the form of a key. Except for primitiveness of vessels, wood of Chloranthaceae is very similar to that of Lactoridaceae and Piperaceae, and this probably indicates a close phyletic relationship. The large rays of chloranthaceous wood, little modified from primary rays and with upright cells predominantly , are indicative of some degree of herbaceousness and some degree of secondary woodiness. Scattered bundles and multilacunar nodes, characteristics of monocotyledons, are absent in Chloranthaceae but present in Piperaceae. The sympodial habit of Chloranthus and Sarcandra, and the presence of vessel s in roots but not in sterns of Sarcandra are conditions like those basic to origin of monocotyledons. The possibility that Chloranthaceae are close to Piperales and that these groups are close to origin of monocotyledons should be considered. Some cladists have hypothesised that secondary vessellessness is polyphyletic in dicotyledons. While these cases are theoretically possible, the histological and ecological seenarios that must be hypothesised for these events are ignored by cladists; most of these seenarios are unlikely for reasons explored here, although a few are still worthy of consideration. Stern endodermis is reported for three species of Chloranthus.