Wood Anatomy of Crossosomatales: Patterns of Wood Evolution with Relation to Phylogeny and Ecology

The seven families hypothesized by Sosa and Chase to comprise Crossosomatales possess relatively long vessel elements with scalariform perforation plates and scalariform to opposite vessel-ray pitting; tracheids; diffuse axial parenchyma; and heterogeneous rays. These and other primitive character states do not indicate relationships, but they do not offer any evidence against the idea that Crossosomatales are a natural order. Departures from the primitive character states are related to ecological adaptations. Crossosomataceae have simple perforation plates (scalariform briefly at the beginning of the secondary xylem), a feature correlated with the seasonal aridity of habitats occupied by the family, the sole family of the order to exhibit such an ecological shift. Presence of tracheids (which confer embolism resistance to a wood) in ancestors of Crossosomataceae probably pre-adapted the family for entry into highly seasonal habitats. Minimal vessel grouping in all other genera shows that tracheid presence deters vessel grouping; tracheid presence also deters shortening of vessel elements. Autapomorphies are shown by Aphloiaceae (tracheid dimorphism, rays of two distinct widths); Crossosomataceae (perforation plates predominantly simple, lateral wall pitting of vessels alternate); Geissolomataceae (wide rays); Ixerbaceae (fiber-tracheid tendency); Staphyleaceae (adjacence of axial parenchyma to vessels); Stachyuraceae (simplification of perforation plates); and Strasburgeriaceae (large cell size). Although tracheid presence seems plesiomorphic in Crossosomatales, a degree of lability in density and size of bordered pits on imperforate tracheary elements probably occurs within this order and in other dicotyledon groups

Tracheid Dimorphism: A New Pathway in Evolution of Imperforate Tracheary Elements

Certain dicotyledon families characteristically have tracheids as their imperforate tracheary element type. Of these, six families are anomalous by having septate (or nonseptate but living) fiber-tracheids or libriform fibers coexisting with the tracheids in some species or genera (Austrobaileyaceae, Celastraceae, Convolvulaceae, Ericaceae, and Grossulariaceae, and Rosaceae). Data from the literature and original data on wood anatomy of these families are presented. A theory of tracheid dimorphism is developed to account for these instances of tracheids combined with fiber-tracheids or libriform fibers. According to this theory, septate or living fiber-tracheids or libriform fibers are produced in addition to tracheids, starting with ancestors that contain tracheids as the only imperforate tracheary element type, in response to selection for a rapidly increased photosynthate storage capacity, while maintaining the advantage of tracheids in providing conductive safety. Borders are phyletically lost rapidly on the septate (or nonseptate but living) imperforate tracheary elements because they are not water-conducting cells. Genera cited in this stud y can be ranged into a phyletic series with respect to differentiation from the hypothetical monomorphic-tracheid ancestors with respect to (I) loss of borders on pits of the septate or living elements; (2) distribution of tracheids with respect to vessels; and (3) retention of axial parenchyma. Austrobaileya is the most primitive genus in these respects, while genera such as Holodiscus and Spiraea are specialized. Tracheid dimorphism is compared to vessel dimorphism, fiber-tracheid dimorphism, fiber dimorphism, and the dimorphism related to origin of vessels. All these pathways except the last named one are confined to small numbers of families, and are considered minor trends superimposed on the major trends described by I. W. Bailey and coworkers. Basic to all of the dimorphic behaviors described is selection for two divergent cell types as a way of performing two distinctive wood functions

Wood and Stem Anatomy of Phytolaccoid and Rivinoid Phytolaccaceae (Caryophyllales): Ecology, Systematics, Nature of Successive Cambia

Quantitative and qualitative wood features are presented and analyzed for seven species of subfamily Rivinoideae and four of subfamily Phytolaccoideae. All species have nonbordered perforations plates, as elsewhere in suborder Phylocaccineae. Libriform fibers characterize both subfamilies, but vasicentric tracheids occur in two rivinoid species. Axial parenchyma is vasicentric scanty (apotracheal bands and patches in one species). Rays are mostly multiseriate, with procumbent cells infrequent in most species. Rivinoids and phytolaccoids differ from each other in ray height and width and in crystal types. The xeromorphic wood of Petiveria and Rivina is related to their short duration (woody herbs) in disturbed soil that dries readily. Woods of other genera are moderately mesomorphic, correlating with seasonally tropic habitats. Genera of Phytolaccaceae studied here have the same ontogenetic features leading to successive cambia as Stegnosperma. Phytolacca dioica has amphivasal pith bundles in which secondary growth occurs. Vessel restriction patterns are newly reported for the family

Trematolobelia: Seed Dispersal; Anatomy of Fruit and Seeds

The endemic Hawaiian genus Trematolobelia (Lobeliaceae, or Campanulaceae, subfamily Lobelioideae) was erected on the basis of its distinctive fruit. This fruit has a seed-dispersal mechanism unique in the family. Assertions have been made by some workers that holes in the fruit wall are the work of insects, and are not related to the dispersal mechanism. This contention has been adequately disproved by other investigators, but, in fact, the precise nature of the dispersal mechanism and the anatomical structure responsible for its action have never been adequately described. In addition, the present study reveals the potential taxonomic use of capsular anatomy, a feature of importance because various authors recognize one, two, or three species in the genus. These species are based largely on floral features or foliar characteristics, and not on those of the fruit. Unusually good material of Trematolobelia collected by the writer during the summer of 1958 provides a sufficient basis for presenting the features mentioned above in some detail

Wood Anatomy of Scytopetalaceae

Eight wood samples representing six species in two genera of Scytopetalaceae are examined with respect to qualitative and quantitative features. Rhaptopetalum differs from Scytopetalum by having scalariform perforation plates, fiber-tracheids, longer vessel elements, and a series of features probably related to the understory status of Rhaptopetalum is compared to the emergent nature of Scytopetalum. Features ofScytopetalaceae relevant to relationships of the family include (I) scaJariform perforation plates; (2) alternate medium-sized intervascular pits; (3) scalariform vessel-parenchyma pitting; (4) diffuse-in-aggregates and scanty vasicentric axial parenchyma; (5) axial parenchyma strands subdivided in places into chains of chambered crystals; and (6) rays that are high, wide, heterogeneous, and with erect cells comprising uniseriate rays. These features are compared for a number of families alleged by recent phylogenists to be related to Scytopetalaceae. Scytopetalaceae appears best placed in Theales, nearest to such families as Caryocaraceae, Lecythidaceae, Ochnaceae, Quiinaceae, and Theaceae, although Rosales (e.g., Cunoniaceae) must be cited also on account of numerous resemblances in wood anatomy

Wood Anatomy of Fouquieriaceae in Relation to Habit, Ecology, and Systematics; Nature of Meristems in Wood and Bark

Qualitative and quantitative data are presented for wood of all species of Fouquieriaceae, the samples selected so as to cover important variables with respect to organography and age. Wood contains fibertracheids (plus a few vasicentric tracheids). Diffuse axial parenchyma is mostly grouped as diffuse-in-aggregates or diffuse clusters (new term), with transitions to pervasive axial parenchyma in some species. Rays are Heterogeneous Type II. These wood features are relatively unspecialized and are consistent with placement of the family in Ericales s.1. as defined in recent DNA-based cladograms. Xeromorphic wood in nonsucculent species occurs only in Fouquieria shrevei; the lateral branches of F. columnaris also have xeromorphic wood. If the preceding two instances and proliferated parenchyma of the three succulent species (F. columnaris, F. fasciculata, and F. purpusii) are excluded from quantitative studies, wood of Fouquieriaceae is rather mesomorphic, despite the habitats occupied by the family. This paradox is explained by the very sensitive drought deciduousness. Also, the succulent species produce water-storage parenchyma by means of expansion of rays and axial parenchyma bands. Details of these two types of meristems, as well as three other types of meristems within wood (not including vascular cambium) and four bark meristems (other than phellogen) are described; five of these meristems are newly reported for the family. Wood data permit recognition of both the three succulent and eight nonsucculent species within a single genus, in agreement with Henrickson (1972), but few wood features offer species characters. Most wood features, including the abundant reaction wood, are closely related to habit, organography, and ecology

Wood and Bark Anatomy of Degeneria

Wood anatomy of the recently described Degeneria roseiflora differs from that of D. vitiensis by possessing narrower vessels, much thicker-walled vessels and fiber-tracheids, abundant uniseriate rays, and greater numbers of ethereal oil cells in rays. Because both large and smaller wood samples of D. vitiensis were studied, ontogenetic changes in the wood are presented and separated from those features that probably vary with the species. Tyloses and perforated ray cells are newly reported for Degeneria. Anatomy of mature bark of D. roseiflora is described. Wood anatomy of Degeneria is moderately primitive. Although Degeneria is often compared to Himantandraceae and Magnoliaceae, Eupomatiaceae also seem very close, if not closer

Diagonal and Tangential Vessel Aggregations in Wood: Function and Relationship to Vasecentric Tracheids

The list of families with diagonal ( dendritic or flamelike of other authors) patterns of vessel aggregation is similar to the list of families that have vasicentric tracheids. This paper attempts to deal with apparent exceptions. Because of recent reports of vasicentric tracheids, the families with diagonal vessel aggregations are all also on the list of families with vasicentric tracheids with the exception of four families. Genera of those four families are studied to see if a relationship between vasicentric tracheids and diagonal vessel aggregations does hold. Of the families not on both lists, Leitneriaceae (Leitneria), Melastomataceae (Mouriri), and Moraceae (Madura) do prove to have vasicentric tracheids in appreciable numbers. Small numbers of vasicentric tracheids and small degrees of vessel aggregation occur in Asimina (Annonaceae), Morus (Moraceae), and various Araliaceae. Vessels may not appear diagonally grouped if libriform fibers accompanying them are few, or if vessels are separated by large numbers of vasicentric tracheids. Diagonal grouping appears most marked in woods from drier and colder localities. Extensive diagonal vessel aggregations are apparently a reliable indication ofvasicentric tracheid presence, but only a portion of the woods with vasicentric tracheids have diagonal vessel aggregations. By having few, large, and intersecting aggregations of vessels mixed with vasicentric tracheids, a wood has greater potential safety (failure of fewer water columns by air embolisms) in space (within wood) and time than a wood with smaller, more numerous vessel groupings. Vessel grouping and vasicentric tracheid presence are considered additive in their safety effects

Wood Anatomy of Resedaceae

Quantitative and qualitative data are presented for seven species of four genera of Resedaceae. Newly reported for the family are helical striations in vessels, vasicentric and marginal axial parenchyma, procumbent ray cells, and perforated ray cells. Wood features of Resedaceae may be found in one or more of the families of Capparales close to it (Brassicaceae, Capparaceae, Tovariaceae). Lack of borders on pits of imperforate tracheary elements is likely a derived character state. Wood of Reseda is more nearly juvenile than that of the other genera in ray histology; this corresponds to the herbaceousness of Reseda. The quantitative features of wood of Resedaceae are intermediate between those of dicotyledonous annuals and those of dicotyledonous desert shrubs. Wood of Resedaceae appears especially xeromorphic in narrowness of vessels, a fact related to the subdesert habitats of shrubby species and to the dry conditions in which annual or short-lived perennial Resedaceae flower and fruit