Rolf Rutishauser

STRUCTURAL AND DEVELOPMENTAL DIVERSITY IN PODOSTEMACEAE (RIVER-WEEDS)

Abstract The structural and developmental diversity of the Podostemaceae is remarkable. A comparison of 19 genera (of 48 genera), and 27 species (of 270 species) is presented, covering both subfamilies, the Podostemoideae (= Pod.) and Tristichoideae (= Trist.). Assuming the Podostemaceae to be derived from a typical cormophytic plant with the classical root-shoot (CRS) model, then evolutionary dynamics of vegetative structures in this family include: formation of green crustaceous structures as a result of dorsiventral flattening of roots, stems or both, reduction and loss of root caps, occurrence of sticking rhizoids and often disk-like holdfasts, and heterotopy of organ formation (from exogenous to endogenous bud formation). Some examples of structural dynamics are unique to certain taxa, e.g. 90° switch of the dorsiventrality plane in leaves of Marathrum, Mourera , and Oserya (Pod.); positional correlation of dithecous leaves (i.e. leaves with two sheaths) and dichotomous shoot branching in Podostemum and genera mentioned above (Pod.); occurrence of unique leaf-shoot mosaics (called ramuli) in Tristicha and allies (Trist.). Thus, the structural categories of typical flowering plants are transcended in the Podostemaceae due to developmental changes and saltational evolution. An overview of reproductive traits in Podostemaceae is given, focussing on characters that are useful in traditional systematics: shape, texture, and dehiscence of spathella (Pod.); presence and shape of cupule (Trist.). Starting with neotropical taxa showing radial flower symmetry (e.g. Rhyncholacis, Marathrum pro parte), most Podostemoideae can be derived by reduction of the number of stamens and basal fusion of the two remaining stamens. Most podostemads are wind-pollinated or autogamous. A few neotropical genera such as Mourera (Pod.) and Weddellina (Trist.) show polyandry, probably as an adaptation to insect-pollination. Other taxonomically used characters such as pollen (dyads in many Pod.), ovules, seeds, and capsules (ribs, dehiscence) are also demonstrated and discussed.

Phylogeny of the clusioid clade (Malpighiales): Evidence from the plastid and mitochondrial genomes

PREMISE OF THE STUDY The clusioid clade includes five families (i.e., Bonnetiaceae, Calophyllaceae, Clusiaceae s.s., Hypericaceae, and Podostemaceae) represented by 94 genera and ≈1900 species. Species in this clade form a conspicuous element of tropical forests worldwide and are important in horticulture, timber production, and pharmacology. We conducted a taxon-rich multigene phylogenetic analysis of the clusioids to clarify phylogenetic relationships in this clade. METHODS We analyzed plastid (matK, ndhF, and rbcL) and mitochondrial (matR) nucleotide sequence data using parsimony, maximum likelihood, and Bayesian inference. Our combined data set included 194 species representing all major clusioid subclades, plus numerous species spanning the taxonomic, morphological, and biogeographic breadth of the clusioid clade. KEY RESULTS Our results indicate that Tovomita (Clusiaceae s.s.), Harungana and Hypericum (Hypericaceae), and Ledermanniella s.s. and Zeylanidium (Podostemaceae) are not monophyletic. In addition, we place four genera that have not been included in any previous molecular study: Ceratolacis, Diamantina, and Griffithella (Podostemaceae), and Santomasia (Hypericaceae). Finally, our results indicate that Lianthus, Santomasia, Thornea, and Triadenum can be safely merged into Hypericum (Hypericaceae). CONCLUSIONS We present the first well-resolved, taxon-rich phylogeny of the clusioid clade. Taxon sampling and resolution within the clade are greatly improved compared to previous studies and provide a strong basis for improving the classification of the group. In addition, our phylogeny will form the foundation for our future work investigating the biogeography of tropical angiosperms that exhibit Gondwanan distributions.

Polymerous Leaf Whorls in Vascular Plants: Developmental Morphology and Fuzziness of Organ Identities

In vascular plants there are at least eight ways to develop polymerous whorls, i.e., whorls with four or more leaves. Six ways are presented and compared with literature to estimate organ identity (morphological significance) of the leaflike whorl members. New shoots (also seedlings) may start with dimerous or trimerous whorls. Then leaf number per whorl rises as follows: (1) Many taxa add more leaves per whorl continuously with increasing size of the apical meristem (e.g., Equisetum, Hippuris). (2) Taxa provided with interpetiolar stipules replace their stipules by leaves (e.g., Galium and allies). (3) Taxa with the capacity to form compound leaves shift basal leaflets around the whole node (e.g., Limnophila, probably also Ceratophyllum). Various whorled plants start shoot development with leaf inception along a helix, which is continued into the whorled region. Then polymerous whorls develop as follows: (4) Acacia longipedunculata forms helically arranged fascicles instead of single leaves before the production of complete whorls. (5) Acacia baueri and Acacia verticillata add supernumerary leaves between a first series of helically arranged leaves. (6) Hydrothrix produces an annular bulge around the node of each first‐formed leaf. All additional leaves of a whorl arise on this annular bulge. Leaf identity of whorl members cannot be defined unequivocally in whorls with asynchronous (i.e., nonsimultaneous) development, dorsoventral distribution of lateral buds, and/or fewer vascular traces than leaves per node. It is heuristically stimulating to accept structural categories (e.g., shoot, leaf, leaflet, stipule) as fuzzy concepts, as developmental pathways that may overlap to some degree, leading to developmental mosaics (intermediates). For example, the whorled leaves of Utricularia purpurea resemble whole shoots, corroborating Arbers partial‐shoot theory.

The architecture of Mourera fluviatilis (Podostemaceae): developmental morphology of inflorescences, flowers, and seedlings.

Mourera fluviatilis from northern South America is a spectacular member of the Podostemaceae (river-weeds). Its raceme-like inflorescences are up to 64 cm long and have 40-90 flowers arranged in two opposite rows. Inflorescence development starts with the initiation of a double-sheathed (dithecous) bract in a terminal position. All lateral bracts (again dithecous) are initiated in basipetal order along the two flanks of the inflorescence. Each gap between two neighboring bracts contains a single flower. The flowers are bisexual, each with a whorl of 16-20 ligulate tepals and 14-40 stamens, which are arranged in one or two whorls. Floral development starts with the formation of a girdling primordium rim around a two-lobed primordial gynoecium. Stamen and tepal initiation is centrifugal on the girdling primordium. The anthers are introrse or extrorse, depending on stamen position. Seedlings develop two entire, threadlike cotyledons, followed by forked filamentous leaves, which arise from the plumular pole. The radicular pole of the hypocotyl develops into a claw-shaped holdfast that fixes the young plant to the rock. The developmental morphologies of Mourera fluviatilis and other members of the Mourera group (including Lonchostephus and Tulasneantha) fit well with the Podostemoideae bauplan known from other New World genera, such as Apinagia and Marathrum.

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 New World 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.

Comparative Morphology and Molecular Systematics of African Podostemaceae‐Podostemoideae, with Emphasis on Dicraeanthus and Ledermanniella from Cameroon

The Podostemaceae (eudicots, Malpighiales) are adapted to rivers that exhibit distinct high‐low water seasonality, mainly in the tropics. They attach to submerged rocks with ribbonlike or crustose green roots that cover the substrate like a carpet. Pronounced root dorsiventrality resulted in disklike crusts lacking root caps. African Podostemoideae show a bewildering array of forms not known from other flowering plants, such as (i) foliage leaves having a basis with two sheaths (e.g., Ledermanniella linearifolia), (ii) modular shoot construction with repeated stem cups (Ledermanniella ledermannii), (iii) endogenous origin of flowers along stems (Dicraeanthus africanus), and (iv) epiphyllous flowers (Ledermanniella letouzeyi). Important morphological transformations specific to African podostemoids include a shift from erect to inverted flowers in the spathella and unilocular ovaries arising via septum loss. New matK sequence data and new morphological data for eight African Podostemaceae species of the genera Dicraeanthus, Djinga, and Ledermanniella are combined with previously published sequences representing all major groups to test the placement of the African taxa in the family. All podostemoids studied from continental Africa form a clade that is sister to the Madagascan genera Endocaulos and Thelethylax. The sister of this African‐Madagascan lineage is the clade comprising all Asian podostemoids and the American genus Podostemum, whereas all other New World podostemoids and the subfamily Tristichoideae are more basal.

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 tribes.

THE PHYLLOTAXY OF COSTUS (COSTACEAE)

The spiromonostichous phyllotaxy of Costus, and other Costaceae, is characterized by low divergence angles, often as low as (30⚬-) 50⚬. This constrasts with the main series Fibonacci (divergence angles approximating 137.5⚬) or distichous phyllotaxy found in all other Zingiberales. A morphological and developmental study of three species of Costus revealed a number of facts about this unusual phyllotactic pattern. In C. scaber and C. woodsonii the divergence angles gradually change along a shoot, from 140⚬-100⚬ in the region of the cataphylls to 60⚬-45⚬ in the inflorescence. In C. cuspidatus, the divergence angles change from 40⚬-100⚬ in the cataphyll region to ca. 137⚬ in the inflorescence. In all three species, the cataphylls and foliage leaves have tubular sheaths, while the inflorescence bracts are nonsheathing. Thus, spiromonostichy is only loosely correlated with closed leaf sheaths.

Morphology and development of the female flowers in Geonoma interrupta (Arecaceae).

Morphology and development of the female flowers in Geonoma interrupta are described and compared with other taxa within Arecaceae. Inflorescences are pleiothyrses. Cincinni are immersed in pits and arranged according to the Fibonacci pattern along the rachillae. The gynoecium is composed of three free carpels in early stages and later becomes pseudomonomerous. Two carpels are sterile; they develop to different degrees and are commonly unequal in size. The fertile carpel contains a single, crassinucellate, anatropous ovule. Styles are formed in each carpel. The style of the fertile carpel becomes basifixed as the ovary enlarges. The stigmas remain free and plicate during development and expose unicellular papillae at anthesis. Pollen tube transmitting tracts and a compitum are present in the ventral slits of the stigmas and the postgenitally united styles during anthesis. A septal nectary is formed by incomplete union of the flanks of the carpels at the base of the gynoecium, and nectar is secreted from an epithelium. It is suggested that in Geonoma as a whole, the attraction of pollinators to female flowers is due to a combination of nectar reward and partial mimicry of male flowers.

Developmental morphology of Ledermanniella bowlingii (Podostemaceae) from Ghana

Abstract. Ledermanniella (c. 44 species) is the largest podostemoid genus in Africa. This paper deals with the structure and development of the Ghanaian species Ledermanniella bowlingii (J.B. Hall) C. Cusset (subgenus Ledermanniella). Characters typical for L. bowlingii include: green ribbon-like roots with exogenous lateral roots and endogenous shoots up to 120 cm; most leaves 3–7 times forked, with intrapetiolar stipules; flowers solitary or in clusters, borne on elongate stems or directly on roots; each flower bud inverted within a spathella; flowers unistaminate; tricolpate pollen in dyads; ovary mainly unilocular but bilocular at the base due to a rudimentary septum; mature capsule with eight ribs, 1.0–1.8 mm long, containing 12–34 seeds, dehiscing by two equal valves; capsule stalk with pedicel (10 mm) and gynophore (2 mm); silica bodies absent in all plant parts. Several characters of L. bowlingii are described here for the first time. The paper shows that accurate morphological analyses of African Podostemaceae are badly needed.