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Summary was undertaken in an attempt to help clarify the relationships of the genus. Detailed descriptions of leaf, stem, nodal, wood, and floral anatomy are presented. Wood is characterized by a combination of solitary and grouped vessels with elements having few-barred scalariform perforation plates, imperforate tracheary elements with very reduced pit borders, exceptionally tall and broad hetero- cellular rays, and vasicentric axial parenchyma. Of special interest is the presence in Sanango of a very uncommon multilacunar nodal structure having split-lateral traces. Stems possess cortical vascular bundles. Leaf stomata are anisocytic and distributed in clusters on the undersurface of the lamina. Anatomical evidences suggest that Sanango is most closely related to the Scrophulariales, sharing many important features with the Gesneriaceae.

The floral and vegetative anatomy of the small Australian genus Aphanopetalum were studied. Wood is described for the first time and is characterized by predominantly solitary pores, scalariform vessel element perforation plates with low bar numbers, imperforate tracheary elements with distinctly bordered pits, sparse axial parenchyma, and a combination of homocellular and heterocellular rays. Starch occurs in both axial and ray parenchyma of the wood. Stems possess unilacunar, one-trace nodes and the uncommon feature of an endodermis with well-defined Casparian strips. Leaves have anomocytic stomata, a bifacial mesophyll and semicraspedodromous venation or a combination of semicraspedodromous and brochidodromous venation. The tetramerous flowers are apetalous or have minute petals. The compound, half-inferior gynoecium consists of essentially totally united carpels. The pattern of floral vascularization resembles different Saxifragaceae sensu lato in that the compound sepal-plane and petal-plane traces give rise to staman bundles as well as sepal, petal, and carpel wall venation in their respective planes. The ventral ovarian bundles are fused into a single ventral complex that subdivides at the top of the ovary to form ventral bundles and to supply the one ovule in each locule. Vegetative and floral features provide compelling evidence to suggest that Aphanopetalum has its nearest relatives among the Saxifragaceae sensu lato rather than Cunoniaceae. The genus is probably best treated as forming its own subfamily (or family) among the saxifragaean alliance.

All eleven genera of the Styracaceae were examined with respect to floral morphology and anatomy. Floral structure and vascularization are described in detail. Flowers of the family exhibit different degrees and patterns of specialization. All Styracaceae show some degree of basal non-divergence of perianth members, forming a hypanthium that is adnate to the ovary wall to a lesser or greater extent. The extent of reduction and amplification in the number of sepals, petals, stamens, and carpels varies widely among genera, and generally the non-divergence, decrease, or increase in parts is not equally pronounced in the different whorls of the same sower. Genera cannot be readily aligned in an intergrading sequence of morphological advancement. Stamen form and anatomy is variable. A fibrous endothecium ranges from well-developed to weakly formed or absent. A nearly uniform feature of the styracaceous gynoccium is the presence of incompletely septate ovaries. The major points of variation in the floral vascular system relate to the number, mode of origin, and degree of independence of sepallary traces; degree of independence of the androecial vasculature; the level at which the common petal and petaladstamen or sepal and sepalad-stamen bundles separate to their component parts; organization of the ventral ovarian supply; and the occurrence of ventral bundles in the style. Floral vascularization provides evidence that the family was derived from an obdiplostemonous ancestor. A unitegmic ovule is predominant in the family and starch is present in the megagametophyte of some taxa. An unusual feature of the flowers of the Styracaceae is the occurrence of stellate and lignified intraovarian trichomes. Numerous similarities in floral morphology and anatomy between Styracaceae and Ericales are pointed out.

The plant body of a typical angiosperm consists of two major organ systems: the root and the shoot. The shoot is composed of stems, leaves, and flowers, and each major organ in turn is composed of tissues that represent collections of one or more specialized cell types. All growth and organ formation of the plant body are initiated and controlled by regions of active cell division termed “meristems.” Meristems are composed of two categories of cells: the dividing initials and the immediate undifferentiated derivatives of cell division. The derivatives subsequently become differentiated and change into different types of mature cells and tissues. Following fertilization, the plant body begins development as a single-celled zygote that undergoes embryogenesis. After a series of early cell divisions, a globose proembryo is formed. During the later stages of embryo development, the embryonic axis of the plant body is formed along with the root and shoot apical meristems from which the rest of the plant body develops following seed germination. One of the most distinctive structural features of plant cells is the surrounding cell wall, typically composed of carbohydrate cellulose. Cell walls play important roles in plant development, cell-to-cell communication, physiology and environmental adaptation, and stress response.

Plants carry out numerous complex processes constituting their physiology to maintain themselves as living systems. Many of these physiological processes are closely related to plant structure. The basic activities are photosynthesis, respiration, metabolism, nutrition, and translocation and mobilization of water and photosynthetic solutes. The principal functional units of the phloem tissue of flowering plants include the major conducting conduit called the sieve tube element, along with its associated companion cells and a variety of integrating phloem parenchyma cells. The structure of the minor veins plays an important role in the process of loading sugars in the leaves. A symplastic mode of loading is indicated by high numbers of plasmodesmata. In some families, the sheath cells around the minor leaf veins are modified as phloem and xylem transfer cells. These cells are characterized by unlignified wall ingrowths. The leaves of some monocotyledons and dicotyledons possess enlarged vascular bundle sheath cells around the minor veins. The long-distance transport of water from roots to leaves occurs within the xylem in a series of highly specialized cells called tracheary elements.

Gene mutations provide the primary means of understanding gene structure and function in plants. A large number of mutants have been identified that affect a wide range of anatomical traits, ranging from embryogenesis to the adult plant. Numerous mutants have been isolated that directly control the root and shoot development, meristem behavior, epidermal cell formation, root hair and trichome development, and vascular tissue differentiation. Hybridization occurs when two different, naturally occurring plant populations show a breakdown in reproductive isolation and an exchange of genes between diverse individuals takes place. In several cases, the hybrids are more or less intermediate in quantitative features. The Aloineae are a well-defined tribe of the monocotyledonous family Liliaceae that provides an insight into the inheritance of leaf anatomical characters. Wood quality is determined by the combined effects of several interrelated and variable wood properties. Heritable wood properties include the amount of juvenile and mature wood, grain pattern, individual cell size and wall characteristics, and chemical properties of the cell wall. Some wood properties can be manipulated during processing, but others are stable features that can only be altered by a focused tree-breeding program.

This chapter describes the various anatomical responses of higher plants to wounds or infections, and includes an analysis of how plants have evolved growth forms to cope with the changing stress patterns in natural environments. Multiple defenses occur in plants in response to stress and invasion of pathogens. Some of these defenses are structural and are often accompanied by chemical alterations in cells and tissues. Plant defenses can be pre-infectional or post-infectional responses. Defenses can be passive in the sense that they are preformed barriers to infection or active mechanisms of resistance that are formed in direct response to an injury or the activities of harmful invaders. The cuticle provides a very effective passive defense. The principal active anatomical response of plants to wounds and infections is to wall off the injured or diseased region. Lignification of cell walls and callose deposition are other common responses of plant tissues to injury. Several structural features that can potentially increase plant resistance include thickening and lignification of cell walls, and increasing the amount of sclerenchymatous tissue, in addition to foliar pubescence, surface waxes, and mineral accumulation. Laticifers can also serve a defensive function by clogging the mouthparts of insects attempting to feed on a latex-producing plant.

Forensic botany—the use of botanical evidence in courts of law—has proven to be useful in both civil and criminal cases. Evidence obtained from plants—including structural information—has gained wide acceptance as either direct or indirect evidence. The careful microanalysis of plant cells, tissues, or organ fragments at both the light-microscope and scanning-electron-microscope levels can provide compelling evidentiary arguments for resolving a variety of legal questions. Food plants also provide a source of forensic evidence. A record of what the victim ate just before death can be obtained by identifying the plant cells that are present in stomach contents. In some cases, the exact restaurant that served the last meal can also be located. The histological features of wood or wood fragments enable wood to be readily identified by family and genus. Obtaining diet and nutritional information on the domestic and wild herbivores represents a significant major application of plant anatomical research. Detailed food habit data and preferences are important because they relate to animal population size and fluctuation, range, and other complex interrelationships. Histological analysis of the herbivore diet has the advantage that materials can be microscopically examined at any stage of digestion, both recently consumed and as fine particles obtained from stomach contents and fecal droppings.

This chapter deals with details of the internal organization and the arrangement of cells and tissues within the three major organs of the primary plant body: the stem, the leaf, and the root. All stems are characterized by repetitive sequences of external nodes and internodes. The leaves and associated axillary buds are positioned at the nodal regions. Leaves are initiated as lateral protuberances on the domelike stem apex, and they occur in a precise arrangement—or phyllotaxis—on the stem. A mature leaf is composed of a leaf base, a stalk-like petiole, and an expanded, flattened blade called lamina. Some taxa have small, leaf-like structures called stipules, positioned between the petiole and the stem. The outermost layers on both surfaces of the blade constitute the upper and lower epidermis. The roots of a plant are collectively called the root system. Roots are composed of three primary tissue regions: the outermost epidermal layer, a wide middle region called the cortex, and an inner core or stele. The innermost layer of the cortex is the endodermis, and it is composed of cells with lignin-like wall material deposited in bands called the Casparian strip.

This chapter describes the origin and structure of the primary plant body. The postembryonic primary plant body arises from small, organized cell populations termed “meristems” that are located at the tips of the stems and the roots. Meristems are regions of active cell division, enlargement, and differentiation. The vegetative shoot apical meristem of angiosperms has a stratified organization, with two or more outer tunica layers in which cell divisions are primarily all anticlinal or oriented at right angles to the surface. Below the tunica layers is a region of corpus cells in which divisions occur in all planes. Active shoot apical meristems exhibit cytohistological zonation, in which the cells in the central zone are relatively large and divide infrequently as compared to the surrounding peripheral zone cells that divide more rapidly. A rib meristem underlies the central zone. Leaves are determinate organs initiated as groups of cells on the flanks of the shoot apex in precise and stable patterns. Leaf organogenesis commences with coordinated changes in the rate and pattern of cell division and expansion in different regions of the developing primordium.

This chapter focuses on the origin and structure of the secondary plant body. All gymnosperms and most dicotyledons develop lateral meristems, which result in radial growth and are responsible for an increase in the width of the stems and the roots. Growth derived from the lateral meristems is called secondary growth and is composed of secondary tissues. Lateral meristems are termed “cambia” and function as biracial zones composed of initials and derivatives. The vascular cambium adds to the girth of the axis by the production of secondary xylem internally and secondary phloem externally. The outer protective layers of the axis are called periderm and are formed by the cork cambium, or phellogen. The vascular cambium develops a short distance behind the apical meristem. The cambium that forms within the vascular bundle is called fascicular cambium. The interfascicular cambium is initiated somewhat later from the renewed division of the parenchyma cells located between the original vascular bundles. A cambium in which the fusiform initials are overlapping and are of variable length is termed “unstratified.” A specialized stratified or stored cambium occurs when the fusiform initials are of nearly equal length, and are grouped in parallel and horizontal rows.

This report concerns itself with the morphology and anatomy of the stem of flowering plants. Research results dealing with both the primary body and secondary xylem are discussed. For the most part, literature dealing with fossil plants, tissue culture, the phloem, the periderm, and regional, purely descriptive, or applied wood anatomy is not treated. I have made no attempt to summarize systematic conclusions, some of which are reviewed in a previous volume (Kadereit 1989). With few exceptions, this discussion is restricted to literature published in the years 1986–1990. During this interval much new factual information has been obtained which has been responsible for the formation of new morphological concepts as well as the reinforcement, substantial modification, or even abandonment of existing theories on the nature, structure, origin, and evolution of angiosperm stems and tissues.

Five genera and 12 species of Staphyleaceae were examined with respect to systematic floral morphology and anatomy. Detailed descriptions of floral structure and vascularization are provided. Features of systematic and evolutionary importance in the family include the number and type of fusion of floral parts, placentation type, occurrence of a vascularized disk, and the degree of independence of floral vascular traces. Flowers of Tapiscia sinensis lack a disk, and the bicarpellate gynoecium, containing no internal ovarian septation, culminates a trend toward carpel fusion and reduction in ovular number that has resulted in a unilocular structure with a solitary ovule attached to a more derived basal or subbasal placenta. The progressive fusion of floral parts in the Staphyleaceae has been accompanied by the characteristic union of the androecial vascular supply and sepal-plane bundles, which subsequently divide to form an externally situated stamen vasculature and internal sepal strands. Huertea and Tapi...