Developmental Genetics and Morphological Evolution of Flowering Plants, Especially Bladderworts (Utricularia): Fuzzy Arberian Morphology Complements Classical Morphology

This review compares new developmental models on flowering and other vascular plants with evolutionary hypotheses formulated by Agnes Arber (1879-1960) and like-minded botanists. Special emphasis is laid on philosophical basics such as perspectivism, pluralism about evolutionary modelling, continuum way of thinking, and fuzzy logic. Arber's perspective is best labelled as F uzzy A rberian M orphology (FAM Approach). Its proponents (‘FAMmers') treat structural categories (e.g. ‘roots', ‘shoots', ‘stems', ‘leaves', ‘stipules') in vascular plants as concepts with fuzzy borderlines allowing intermediates (including transitional forms, developmental mosaics). The FAM Approach complements Cla ssical Plant M orphology (ClaM Approach), which is the traditional approach in botany. ClaM proponents (‘ClaMmers') postulate that the structural categories of vascular plants are regarded as concepts with clear-cut borderlines and without intermediates. However, during the evolution of vascular plants, the root-shoot distinction and the stem-leaf distinction have become blurred several times due to developmental changes, resulting in organs with unique combinations of features. This happened, for example, in the bladderworts (Utricularia, Lentibulariaceae). When focusing on the ‘leaf', the FAM Approach is identical to Arber's ‘partial-shoot theory of the leaf' and Sinha's ‘leaf shoot continuum model'. A compound leaf can repeat the developmental pathway of the whole shoot, at least to some degree. For example, compound leaves of Chisocheton(Meliaceae) with indeterminate apical growth and three-dimensional branching may be seen as developmental mosaics sharing some growth processes with whole shoots! We focus here on the FAM Approach because this perspective is especially promising for developmental geneticists studying flowering and other vascular plants. Copyright 2001 Annals of Botany Compan

Evo-devo and the search for homology ("sameness”) in biological systems

Developmental biology and evolutionary studies have merged into evolutionary developmental biology ("evo-devo”). This synthesis already influenced and still continues to change the conceptual framework of structural biology. One of the cornerstones of structural biology is the concept of homology. But the search for homology ("sameness”) of biological structures depends on our favourite perspectives (axioms, paradigms). Five levels of homology ("sameness”) can be identified in the literature, although they overlap to some degree: (i) serial homology (homonomy) within modular organisms, (ii) historical homology (synapomorphy), which is taken as the only acceptable homology by many biologists, (iii) underlying homology (i.e., parallelism) in closely related taxa, (iv) deep evolutionary homology due to the "same” master genes in distantly related phyla, and (v) molecular homology exclusively at gene level. The following essay gives emphasis on the heuristic advantages of seemingly opposing perspectives in structural biology, with examples mainly from comparative plant morphology. The organization of the plant body in the majority of angiosperms led to the recognition of the classical root-shoot model. In some lineages bauplan rules were transcended during evolution and development. This resulted in morphological misfits such as the Podostemaceae, peculiar eudicots adapted to submerged river rocks. Their transformed "roots” and "shoots” fit only to a limited degree into the classical model which is based on either-or thinking. It has to be widened into a continuum model by taking over elements of fuzzy logic and fractal geometry to accommodate for lineages such as the Podostemacea

Ever since Darwin: why plants are important for evo-devo research

In this essay, I provide examples of: (i) the presence of fractal properties and a continuum of forms in living organisms; (ii) the potential contributions of plant evo-devo towards a general theory of development encompassing various multicellular organisms; (iii) the “arrival” of a wealth of forms in plants that cannot be explained by natural selection alone. As elucidated by evo-devo studies, evolutionary diversification is also due to, e.g., (epi)genetics, correlation, phenotypic integration, self-organization, and physical constraints. Four kinds of phyllotaxis patterns in vascular plants – from Fibonacci systems with divergence angles around 137.5° to spiral systems with divergence angles below 80° – are described and illustrated: Cycas (gymnosperm), Huperzia (clubmoss), Pandanus (screw palm), and Costus (corkscrew ginger). They serve as examples of morphogenetic variation in plants that call for evo-devo explanations beyond (or prior to) the “survival of the fittest”. Charles Darwin was already convinced that natural selection had not been the only driving force in evolution

Developmental Morphology of New World Podostemaceae: Marathrum and Vanroyenella

Podostemaceae live in swift-running rivers with stony beds, mainly in the Tropics. This article is a comparative study of three Marathrum spp. (M. rubrum, M. schiedeanum, and M. tenue) and the monotypic genus Vanroyenella (with V. plumosa). The study is based on material from Mexico. Marathrum rubrum and V. plumosa are Mexican species, whereas the other two species have wider ranges in Central America. Developmental features of Marathrum and Vanroyenella are described and compared with other NewWorld Podostemoideae. Green prostrate roots with asymmetric caps are fixed to the rock by adhesive hairs. Endogenous shoot buds are formed along the roots. They grow into thalloid (dorsiventrally flattened) stems that serve as holdfasts with adhesive hairs. Many compound leaves are dithecous; i.e., they have two sheaths, arranged in the same plane as the primary pinnae. These dithecous leaves can be called “mother leaves” because they give rise to daughter leaves in both their right and left sheath. One of the two sheaths of a dithecous leaf may be also occupied by a fasciculate inflorescence with one to 13 flowers that develop and open one by one. The close relationship of Marathrum and Vanroyenella (as suggested by molecular data) is corroborated by fundamental morphological similarities. One of the seemingly unique features of Vanroyenella is the feather-like construction of the leaves, with filamentous segments arising directly from the rachis. Essential features of pinnate leaf development, however, are shared with Marathrum spp

Theligonum cynocrambe: Developmental morphology of a peculiar rubiaceous herb

The annual Mediterranean herbTheligonum cynocrambe shows a peculiar combination of morphological characters, e.g., switch from decussate to spiral phyllotaxis with 90-100° divergence, combined with a change from interpetiolar to lateral stipules, anemophily, lack of calyx, flowers often dimerous to trimerous, corolla fused in both male and female flowers, male flowers extra-axillary, with 2-19 stamens per flower, female flowers axillary, with inferior uniovulate ovary, basilateral style and perianth, nut-like fruits with elaiosome. In male flowers the androecium emerges as an (uneven) elliptical rim with a central depression. This common girdling primordium is divided up into several stamen primordia. In male flowers with low stamen number the stamen primordia may occupy the corners alternating with the corolla lobes. There are no epipetalous androecial primordia that secondarily divide into stamens. Male flowers occasionally show a hemispherical base that may be interpreted as remnant of the inferior ovary. In female flowers a ring primordium grows into a tube on which the petal lobes arise. The perianth and style become displaced adaxially by uneven growth of the inferior ovary. The ovary is basically bilocular. The lower region of the ovary is provided with a septum that is overtopped and hidden by the single curved ovule.Theligonum is referred to theRubiaceae-Rubioideae, with theAnthospermeae andPaederieae as most closely related tribe

Developmental morphology of branching flowers in Nymphaea prolifera

Nymphaea and Nuphar (Nymphaeaceae) share an extra-axillary mode of floral inception in the shoot apical meristem (SAM). Some leaf sites along the ontogenetic spiral are occupied by floral primordia lacking a subtending bract. This pattern of flower initiation in leaf sites is repeated inside branching flowers of Nymphaea prolifera (Central and South America). Instead of fertile flowers this species usually produces sterile tuberiferous flowers that act as vegetative propagules. N. prolifera changes the meristem identity from reproductive to vegetative or vice versa repeatedly. Each branching flower first produces some perianth-like leaves, then it switches back to the vegetative meristem identity of the SAM with the formation of foliage leaves and another set of branching flowers. This process is repeated up to three times giving rise to more than 100 vegetative propagules. The developmental morphology of the branching flowers of N. prolifera is described using both microtome sections and scanning electron microscop

Novitates Gabonenses 93: a fresh look at Podostemaceae in Gabon following recent inventories, with a new combination for Ledermanniella nicolasii

Background and aims – Podostemaceae is a family of strictly aquatic plants found in rapids and waterfalls. Despite a recent treatment in the Flore du Gabon, the family remained poorly known, with no major studies including Gabonese collections, and almost no targeted inventories since 1966. We present the first large-scale inventory of this family in Gabon, targeting Podostemaceae throughout the country, providing new additions to the flora of Gabon and many new records of poorly known species. Material and methods – Fieldwork was conducted in Gabon between 2017 and 2021. The collected specimens were primarily preserved in ethanol with associated silica gel-preserved material and photographs. Material available at BR, BRLU, LBV, MO, P, WAG, and Z/ZT was examined. For each species, information on distribution and ecology is presented, as well as a distribution map in Gabon. Key results – The 500 newly collected specimens represent 91.4% of all known collections of Podostemaceae from Gabon. Three taxa are newly recorded for the country, including one genus (Inversodicraea tenax, Ledermanniella schlechteri, and Saxicolella nana). New distribution records are also presented for 13 little-known species. Four taxa are excluded from the Gabonese flora (the genus Dicraeanthus, Inversodicraea ledermannii, Ledermanniella sanagaensis, and Macropodiella garrettii). To date, 20 species belonging to five different genera are known to occur in Gabon. A new combination is proposed for Ledermanniella nicolasii, and Inversodicraea tanzaniensis is now considered as a synonym of Inversodicraea tenax

A Historical Perspective of Bladderworts (Utricularia): Traps, Carnivory and Body Architecture

The genus Utricularia includes around 250 species of carnivorous plants, commonly known as bladderworts. The generic name Utricularia was coined by Carolus Linnaeus in reference to the carnivorous organs (Utriculus in Latin) present in all species of the genus. Since the formal proposition by Linnaeus, many species of Utricularia were described, but only scarce information about the biology for most species is known. All Utricularia species are herbs with vegetative organs that do not follow traditional models of morphological classification. Since the formal description of Utricularia in the 18th century, the trap function has intrigued naturalists. Historically, the traps were regarded as floating organs, a common hypothesis that was maintained by different botanists. However, Charles Darwin was most likely the first naturalist to refute this idea, since even with the removal of all traps, the plants continued to float. More recently, due mainly to methodological advances, detailed studies on the trap function and mechanisms could be investigated. This review shows a historical perspective on Utricularia studies which focuses on the traps and body organization

Developmental morphology of branching flowers in Nymphaea prolifera

Nymphaea and Nuphar (Nymphaeaceae) share an extra-axillary mode of floral inception in the shoot apical meristem (SAM). Some leaf sites along the ontogenetic spiral are occupied by floral primordia lacking a subtending bract. This pattern of flower initiation in leaf sites is repeated inside branching flowers of Nymphaea prolifera (Central and South America). Instead of fertile flowers this species usually produces sterile tuberiferous flowers that act as vegetative propagules. N. prolifera changes the meristem identity from reproductive to vegetative or vice versa repeatedly. Each branching flower first produces some perianth-like leaves, then it switches back to the vegetative meristem identity of the SAM with the formation of foliage leaves and another set of branching flowers. This process is repeated up to three times giving rise to more than 100 vegetative propagules. The developmental morphology of the branching flowers of N. prolifera is described using both microtome sections and scanning electron microscop