Pinnately ramified ensiform leaves in the genus Marathrum, (Podostemaceae-Podostemoideae)

The paper deals with the complex leaves of three species of the aquatic genus Marathrum (M. minutiflorum, M. rubrum and M. schiedeanum). It is shown that they represent pinnately ramified ensiform leaves. The dissection of the leaves contributes to surface enlargement and thus to improvement of their hydrophylls function. The ensiform structure is confirmed by the transverse position of the sheathing lower leaf zone and the subsequent intercalary elongational growth proceeding in the median plane towards the abaxial side of the leaf (upper leaf zone). The petiole continues into the rachis-like central axis of the blade from which pinnate-like segments diverge at the adaxial and abaxial edge of the ensiform blade. The segments give rise to tufts of clavate enations that end in long filaments. The filigree pinnately segmented ensiform leaves of Marathrum are interpreted as a further development of the fan-shaped and irregularly lobate ensiform leaves occurring in Mourera and Apinagia. Pinnately ramified ensiform leaves obviously evolved in convergence to the common type of pinnate leaves found in angiosperms.     

Alternative modes of leaf dissection in monocotyledons

Although a majority of monocotyledons have simple leaves, pinnately or palmately dissected blades are found in four orders, the Alismatales, Pandanales, Dioscoreales and Arecales. Independent evolutionary origins of leaf dissection are indicated by phylogenetic analyses and are reflected in the diversity of mechanisms employed during leaf development. The mechanism of blastozone fractionation through localized enhancement and suppression of growth of the free margin of the leaf primordium occurs in the Araceae and Dioscoreaceae. By contrast, the corrugated, dissected leaves of palms (Arecaceae) develop through a two-step process: first, plications are formed through intercalary growth in a submarginal position and, second, the initially simple leaf blade is dissected through an abscission-like process of leaflet separation. A third mechanism, perforation formation, is employed in Monstera and five related genera of the Araceae. In this mode, discrete patches of cells undergo programmed cell death during lamina development, resulting in formation of open perforations. When perforations are positioned near the leaf margin, mechanical disruption of the thin bridges of marginal tissue results in a deeply pinnatisect blade. Whereas blastozone fractionation defines the early primary morphogenesis phase of leaf development, the other two modes occur later, during the secondary morphogenesis/histogenesis phase. Evolution of these mechanisms presumably has involved recruitment of other developmental programmes into the development of dissected leaves.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 25–44.     

Developmental morphology of Apinagia multibranchiata (Podostemaceae) from the Venezuelan Guyanas

Apinagia (c. 50 spp.) is the largest genus of American Podostemaceae. Apinagia multibranchiata (Matth.) Royen is a haptophyte endemic to the Venezuelan Guyanas. It fits well with the Podostemoideae bauplan known from other New World genera, such as Marathrum and Mourera. Shoots arise in pairs from filamentous creeping adhesive roots. During the rainy season submerged vegetative shoots grow up to more than a metre long. They are normally unbranched and provided wihdistichously arranged leaves which are laterally flattened into one plane. The lanceolate leaves may show a fimbriate tip. Tufts of threads are found on the upper leaf surface which faces the sky. When the water recedes in December-January, ascending reproductive shoots (up to 15 cm long) are formed which branch syrnpodially. The first module produces a variable number of leaves. Distal leaves are often double-sheathed (dithecous). Their inner sheaths are fused into a tube that covers the first flower bud. Daughter modules arise from the outer sheaths of the distal leaves. These modules consisting of two double-sheathed leaves and a flower are repeated giving rise to 2–15 stalked flowers. The flowers are entomophilous and provided with 6–29 pink stamens. Architecture and developmental morphology of A. multibranchiata are compared with other members of the genus.     

The ramification of Apinagia riedelii: A key to the understanding of the plant architecture of Podostemaceae,subfamily Podostemoideae

The study of the ramification pattern of Apinagia riedelii results in a new concept of the architecture of this species, with general implications to members of subfamily Podostemoideae with dithecous leaves. The presence of a subtending leaf below the floriferous shoot proves axillary branching also for species with dithecous leaves. Previous opinions of an unusual ramification mode by subfoliar or non-axillary branching or stem bifurcation in combination with dithecous leaves hitherto pleaded for Podostemoideae is refuted. Moreover, the view of the so-called dithecous leaves with one sheath (theca) at the ventral and one at the dorsal side of the leaf, previously regarded as initially connected with branching, has to be changed. The dithecous leaf arises from the branch and not from the mother shoot axis – as previously believed – and represents the addorsed hypsophyll, i.e., the first leaf (prophyll) of the floriferous branch. This finding leads to the conclusion that the lower sheath of the dithecous leaf is the ventral (not dorsal) sheath pointing to the branch and surrounding its flower bud with a ligule or an ochrea and a hood upon the bud. In this way, the branch and its flower bud become seemingly sunk in the leaf base. At the fusion of leaf basis and shoot results this enigmatic common tissue. The wings of the dorsal (upper) sheath of the dithecous leaf point to the mother shoot axis of the branch. Successive floriferous branches along the main stem disclose the shoot axis of A. riedelii as a monopodium (not sympodium) that develops an anthocladial (foliated) inflorescence in the form of a botrys or a compound botrys, respectively. Since it is generally difficult to define cymose or racemose inflorescences if subtending leaves are absent – which occur in most other species of subfamily Podostemoideae with dithecous leaves – the nature of these inflorescences is discussed anew. The findings on A. riedelii have consequences on our comprehension of the shoot architecture of Podostemoideae.     

Comparative studies in the morphology of Crenias weddelliana and Maferria indica with reference to Sphaerothylax abyssinica (Podostemaceae: Podostemoideae)

The scope of morphological plasticity of vegetative structures among Podostemoideae (Podostemaceae) is documented for Crenias weddelliana, a neotropical species, Maferria indica, a palaeotropical species, and Sphaerothylax abyssinica, from Kenya, and compared with related taxa. The study highlights intrinsic characters of the widely enigmatic plant body of many species of the subfamily Podostemoideae. These include dorsiventrality of shoots occurring irrespective of gravity, incurvate distichy and one‐sided spirodistichy correlated with shoot dorsiventrality, asymmetric leaves, and several types of positioning of the two prophylls and inflorescence structures. The homogeneity of hairs of the ‘Zeylanidium olivaceum type’ established on the subulate leaves of some Indian species is of taxonomic value. The latter also applies to the stipella (not stipule) on the asymmetric compound leaf in New World species. The morphological data represent a framework of features consistent for the subfamily. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 138 , 63–84.     

A new species of the Brazilian genus Chresta (Asteraceae, Vernonieae) from Bahia

A new species of the genus Chresta Vell. ex DC. (Vernonieae, Asteraceae) from the Brazilian state of Bahia is described and illustrated. The new species resembles Chresta pinnatifida (Philipson) H.Rob. but differs in having solitary glomerules, leaf bases clasping the stem and 35–40 capitula per glomerule. It can be distinguished from Chresta harleyii and Chresta martii , the other two species of the genus with pinnately lobed leaves, by the type of pubescence, leaf blade bases and florets number. In addition, a key to distinguish all the species of the genus is presented. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 587–590.     

Leaf architecture and ecophysiology of an early basal eudicot from the Early Cretaceous of Spain

Iterophyllum lobatum gen. et sp. nov. is reported from the late Barremian lithographic limestones of Las Hoyas, Spain. It consists of a simple, petiolate leaf, with a pinnately lobed lamina. The dentate thickened margin bears chloranthoid‐like glands at lobe apices and sinuses. The venation is pinnate and craspedodromous, with three discernible vein orders. Based on the low regularity of vein course and angles and the low leaf rank, such a venation pattern may represent an early evolved leaf archetype in early basal eudicots. An acropetal leaf development mode in I. lobatum is similar to that in several living Papaveraceae. The leaf architecture and ecophysiology, particularly the vein widths and the glands, indicate that I. lobatum leaves were aerial. The plant grew close to water in the wetland terrestrial ecosystem of Las Hoyas. Iterophyllum lobatum might have been an opportunist species in early ecological succession stages after wildfires. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 594–605.     

Enigmatic morphology of Djinga felicis (Podostemaceae – Podostemoideae), a badly known endemic from northwestern Cameroon

Djinga is a monotypic genus restricted to the Cameroon Ridge (‘Dorsale Camerounaise’) of NW Cameroon. Besides the type locality Mount Djinga (Adamawa Province, near Tignère), it also grows in waterfalls near Mount Oku (NW Province). This paper describes the structure and development of Djinga felicis using scanning electron microscopy and microtome sections. Cusset's protologue is enriched considerably. Roots are green, dorsiventrally flattened and adherent to submerged rocks. They are broad ribbons or crusts (up to 1 cm broad) which branch exogenously. Root‐borne shoots (up to 17 cm) have filamentous leaves with sheaths and (occasionally) attached stipules. Flowers are borne as part of reproductive short shoots which arise exogenously along the stems and endogenously along the roots. Djinga shows non‐axillary stem branching. Reproductive shoots along the main stem usually stay short. They arise from the abaxial side of double‐sheathed leaves, a key innovation of Podostemoideae. These short shoots shift into pocket‐like stem positions clearly below their associated leaves. Each flower bud inside a spathella is erect, but with an inclined ovary. The flowers are unistaminate with a broad connective. Unlike many other Podostemoideae, the tricolpate pollen grains are arranged in both dyads and monads. The ovary is globular and unilocular. The mature 8‐ribbed capsule dehisces by two slightly unequal valves, releasing 40–50 seeds. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 64–81.     

Shoot and compound leaf comparisons in eudicots: dynamic morphology as an alternative approach

Recent developmental studies suggest that the compound leaf is a more or less incompletely developed shoot. Instead of treating compound leaves and shoots as non-homologous, this interpretation draws a continuum between them. The present work considers the plant as a hierarchical series of units on which similar developmental processes are at work, and where each level (shoot, compound leaf, leaflet) is 'repeated' by the next higher level. Measurements related to the expression of developmental processes operating on leaves at the shoot level and on leaflets at the compound leaf level were used to determine if similar processes are at work at these different levels during early stages of organogenesis. Plants with compound leaves showing acropetal leaflet inception, representing a total of 16 species from ten eudicot families, were studied. Based on several types of quantitative analyses, there appears to be a continuum between so-called shoots, compound leaves and leaflets in the species studied. This perspective, qualified as dynamic morphology, both parallels and complements the classical interpretation.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 143, 219−230.     

A new species of Achetaria (Plantaginaceae) from south-eastern Brazil

A new species, Achetaria latifolia V.C.Souza, is described and illustrated. It is characterized by its broadly ovate leaves, indument of stems and leaves of noncapitate hairs, and pubescent capsule. Achetaria latifolia is known only in the coastal dune-area of Cabo Frio region, Rio de Janeiro State, Brazil.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 148 , 73–75.     

Expression of SHOOT MERISTEMLESS, WUSCHEL, and ASYMMETRIC LEAVES1 Homologs in the Shoots of Podostemaceae: Implications for the Evolution of Novel Shoot Organogenesis

Podostemaceae (the river weeds) are ecologically and morphologically unusual angiosperms. The subfamily Tristichoideae has typical shoot apical meristems (SAMs) that produce leaves, but Podostemoideae is devoid of SAMs and new leaves arise below the base of older leaves. To reveal the genetic basis for the evolution of novel shoot organogenesis in Podostemaceae, we examined the expression patterns of key regulatory genes for shoot development (i.e., SHOOT MERISTEMLESS (STM), WUSCHEL (WUS), and ASYMMETRIC LEAVES1/ROUGH SHEATH2/PHANTASTICA (ARP) orthologs) in Tristichoideae and Podostemoideae. In the SAM-mediated shoots of Tristichoideae, like in model plants, STM and WUS orthologs were expressed in the SAM. In the SAM-less shoots of Podostemoideae, STM and WUS orthologs were expressed in the initiating leaf/bract primordium. In older leaf/bract primordia, WUS expression disappeared and STM expression became restricted to the basal part, whereas ARP was expressed in the distal part in a complementary pattern to STM expression. In the reproductive shoots of Podostemoideae with a normal mode of flower development, STM and WUS were expressed in the floral meristem, but not in the floral organs, similar to the pattern in model plants. These results suggest that the leaf/bract of Podostemoideae is initiated as a SAM and differentiates into a single apical leaf/bract, resulting in the evolution of novel shoot-leaf mixed organs in Podostemaceae.     

The architecture of Zeylanidium olivaceum (Podostemaceae) inferred from the structure of the primary shoots

Zeylanidium olivaceum (Podostemaceae-Podostemoideae) is the only crustose-rooted species of the genus that still develops prominent primary shoots from the seedling in addition to the secondary (root-borne) shoots forming the clonal plant body. The primary shoots are articulated into an up to 8.5 cm long and 4 mm thick stalk (hypocotyl) and a copiously foliated paint-brush-like shoot which is sympodially branched in the form of a helicoid cyme. The helicoid branching pattern indicates a transversal prophyll position, typical of the dicotyledons, but replaced in most other Podostemoideae by a median prophyll position. The short stems within the leafy head do not separate, but are fused to a dense aggregate (coenosome). Branches are mainly vegetative with a rosette of about 20 elongate subulate leaves. The primary shoots branch in the vegetative stage and thus differ from other Podostemoideae where ramification is confined to the floriferous shoots. The leaves adhere together at the base, forming an apical furrow-like hollow surrounding the shoot tip. The tiny shoot apex is one-layered, radially symmetrical, and develops leaf primordia in a decussate pattern. The erect primary shoots thus differ from the distichously foliated plagiotropic secondary shoots by the decussate phyllotaxis, and by the presence of more than 20 leaves on a shoot as compared to the about six leaves on the vegetative and floriferous secondary shoots. The features observed in the primary shoots are interpreted as primitive as compared to those of the secondary shoots. Z. olivaceum is thus characterised by heterobathmy, i.e., the occurrence of plesiomorphic (primary shoots) and apomorphic features (secondary shoots). The primary shoots exhibit primitive features that apparently have been lost in secondary and primary shoots of most other members of subfamily Podostemoideae.     

Structural analysis of the dissected ensiform leaves and shoot morphology of Marathrum foeniculaceum (Podostemaceae)

Foliage leaves of Marathrum foeniculaceum Humb. & Bonpl. (Podostemaceae–Podostemoideae) resemble pinnate compound leaves at first sight. But the similarity is deceptive, since studies of the leaf structure reveal the ensiform (sword-like) shape of the blade. The ribbon-shaped central rachis-like portion represents the parallel-veined ensiform blade that extends in the median plane direction. Pinnae, typically developing from the leaf margin of the blade in transverse position relative to the mother shoot axis, do not occur here, but instead, bi-pinnate-like appendages arise alternately at the adaxial and abaxial edge of the ensiform blade. The pinnate-like structures are accessory structures. These project only from one side (“front side”) of the ensiform blade. The appendages produce repeatedly forked threads that end in pubescent filaments. The trichomes are of the Zeylanidium olivaceum type. The occurrence of similar structures in species of Marathrum and the related genera Apinagia and Mourera are discussed.     

Development of the floral shoot and pre‐anthesis cleistogamy in Hydrobryopsis sessilis (Podostemaceae)

The reproductive biology of Hydrobryopsis sessilis (Podostemaceae, subfamily Podostemoideae), a reduced, threatened, aquatic angiosperm endemic to the Western Ghats of India, was examined. This is the first report on the transition from the vegetative to the reproductive phase in this plant, describing floral ontogeny, pollination and the breeding system. The cytohistological zonation of the apical meristem of the reproductive thallus is identical to that of the apical meristem of the vegetative thallus. The floral shoots do not replace vegetative shoots (i.e. the vegetative shoots never bear flowers), but form at new sites at the tip of the flattened plant body. Each floral shoot meristem is tiny, deep‐seated and concave and arises endogenously following lysigeny. The floral shoot meristem gives rise to four to six bracts in a distichous manner. The development of spathe, stamens and carpels is described. The ab initio dorsiventrality of the carpels and the occurrence of endothelium in the ovules are reported. The mature stigmas and anthers lie close to each other. The pollen germinates within undehisced anthers and the pollen tubes enter the stigmas in the unopened floral bud, leading to pre‐anthesis, complete, constitutional cleistogamy under water. The seed set is 63.2%. A significant finding is the penetration of several pollen tubes into the filaments of stamens in 16% of the flower buds, indicating a trend towards cryptic self‐fertilization. The Indian Podostemoideae appear to show a shift from xenogamy or geitonogamy or autogamy in a chasmogamous flower to complete autogamy in a cleistogamous flower. The floral modifications leading to cleistogamy in H. sessilis have been identified. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 222–236.     

Leaf anatomy and the occurrence of false veins in Asplenium (Aspleniaceae, Pteridophyta)

False veins in African afro-alpine (2000–4700 m) Asplenium species with long creeping rhizomes and highly dissected leaves are morphologically and anatomically similar to true veins but differ in the absence of a vascular bundle. False veins in Aspleniaceae may have originated by the fusion of leaf lobes, and are more similar to those in Angiopteris and Thelypteris than to those in Davallia and Hymenophyllaceae. Because false veins are long and extend from the leaf margin to the junction of the neighbouring true veins in A. actiniopteroides , A. goetzei , A. majus , A. praegracile , A . sp. nov. and A. uhligii , but short, not reaching this junction in A. decompositum , A. demerkense , A. kassneri , A. linckii and A. mildbraedii , and even absent in A. aethiopicum , A. lademannianum , A. simii , A. stipicellatum and A. volkensii , they can be used for identification in this enigmatic group of ferns.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 187–194.     

Developmental morphology of foliose shoots and seedlings of Dalzellia zeylanica (Podostemaceae) with special reference to their meristems

The developmental morphology of seedlings and shoots of Dalzellia zeylanica was examined with reference to the meristem in order to understand the dorsiventral, foliose shoot. In seedlings, no obvious primary shoot and no root are formed. Subsequent to disappearance of the vestigial primary shoot meristem, two shoot meristems are established in the axils of the cotyledons, one of which grows into a secondary shoot. Microtome and SEM examinations of mature plants show that the shoot meristem is complex, comprising three zones along the shoot margin. The organogenetic zone, equivalent to the shoot apical meristem, produces dorsal leaves proximally and much fewer marginal leaves distally. During development, the zone repeatedly changes into a dorsal zone, while a new organogenetic zone is formed in an area between developing marginal leaves, resulting in the alternation of the organogenetic and dorsal zones, which allowed development of the coenosomic structure of the shoot. The dorsal and ventral zones do not produce leaves, but contribute to shoot expansion. The ventral zone also forces the marginal leaves to shift to the lateral side of the shoot. The rosette with tufted leaves might be a modification of the short shoot (ramulus) of other Tristichoideae.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 289–302.     

Diamantina lombardii – an odd Brazilian member of the Podostemaceae

This paper complements the diagnosis of the recently described genus Diamantina and its only species Diamantina lombardii Novelo, Philbrick and Irgang from Minas Gerais (Brazil). Four new features not known from other Podostemaceae–Podostemoideae are documented by microtome sections and SEM graphs: (i) The digitate foliage leaves lack vascular tissue completely. (ii) Leafy shoots produce one or two flowers in terminal and subterminal position. The spathella subtending the subterminal flower is scale-like and positionally homologous to a digitate bract (leaf), whereas the spathella covering the terminal flower bud is tubular (as usual for Podostemoideae). (iii) The usually rudimentary androecium consists of two stamens which form a complete whorl together with three inconspicuous tepals around the gynophore. (iv) The bilocular ovary has an apical cleft. Each carpel tip (hollow inside) is topped by a prominent horn-like stigma. Additional peculiar features of D. lombardii (already mentioned in Philbrick et al., 2004. Syst. Bot. 29, 109–117) are shown: presence of a prominent gynophore (mainly known from African Podostemoideae), and digitate leaves (as found in Cladopus from Eastern Asia to NE Australia).     

Morphology and development of the subterranean organs of the achlorophyllous Sciaphila polygyna (Triuridaceae)

The subterranean organs of the achlorophyllous Sciaphila polygyna (Triuridaceae) are described, depicted, and structurally explained for the first time. Unlike other Triuridaceae, the subterranean system of S. polygyna appears as a complex star-like structure of short, but thickened, roots as well as scale leaves and shoots. A complete series of sections revealed the following construction. In the axil of a scale leaf at a shoot of first order, a side shoot of second order as well as a pair of endogenous shoot-borne roots arise. This side shoot of second order also develops a scale leaf very early in ontogeny, which again gives rise to a side shoot of third order and a pair of shoot-borne roots. Other scale leaves at shoots of any order may also bear shoots and root pairs. This growth pattern occurs in a very close manner without internode elongation, resulting in the clumped, star-like appearance. The structures described superficially resemble the root systems of many mycoheterotrophic plants from other families. Comparisons with respect to how they develop, however, show that these similar root systems can result from distinct developmental patterns, suggesting independent evolutionary pathways and a considerable evolutionary pressure towards abbreviated and thickened roots in mycoheterotrophic plants. Possible advantages as well as evolutionary implications of the structures described are discussed.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 295–301.     

Two new species of Lessingianthus (Vernonieae, Asteraceae) from the Brazilian highlands

Two additional species of Lessingianthus , L. bakerianus and L. lanuginosus , from the campo cerrado vegetation of central Brazil, are described and illustrated. The first species is characterized by the presence of capitula arranged in groups, nine to 12 florets per head, leaves sessile, oblong to ovate leaf blades with the lower surface densely lanate, sparsely villous on the main veins. It has certain resemblance to L. syncephalus (Sch. Bip. ex Baker) H. Rob. and L. brevipetiolatus (Sch. Bip. ex Baker) H. Rob., which present petiolate leaves and leaf blades lanceolate, cuneate or attenuate at the base. L. lanuginosus is superficially similar to L. buddleiifolius (Mart. ex DC.) H. Rob., but differs in having smooth stems, woolly indumentum, smaller heads and the largest leaves disposed at the middle of the stem.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society, 2006, 150 , 487–493.     

Bauhinia larsenii, a fossil legume from Guangxi, China

Fossil leaves and a branch with a leaf and a pod attached have been discovered from Ningming County, Guangxi Autonomous Region, China, and are described as Bauhinia larsenii sp. nov. (Leguminosae: Cercideae). The strata from which the Bauhinia fossils were collected, namely the Ningming Formation, were dated as Late Eocene–Oligocene based on a combination of pollen, fauna and flora. The affinity of the new species to Bauhinia section Micralvesia subsection Viridescentes species is also discussed.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 437–440.