Molecular phylogenetic relationships among Lemnaceae and Araceae using the chloroplast trnL-trnF intergenic spacer

We test competing hypotheses of relationships among Aroids (Araceae) and duckweeds (Lemnaceae) using sequences of the trnL-trnF spacer region of the chloroplast genome. Included in the analysis were 22 aroid genera including Pistia and five genera of Lemnaceae including the recently segregated genus Landoltia. Aponogeton was used as an outgroup to root the tree. A data set of 522 aligned nucleotides yielded maximum parsimony and maximum likelihood trees similar to those previously derived from restriction site data. Pistia and the Lemnaceae are placed in two separate and well-supported clades, suggesting at least two independent origins of the floating aquatic growth form within the aroid clade. Within the Lemnaceae there is only partial support for the paradigm of sequential morphological reduction, given that Wolffia is sister to Wolffiella+Lemna. As in the results of the restriction site analysis, pantropical Pistia is placed with Colocasia and Typhonium of southeastern Asia, indicative of Old World affinities. Branch lengths leading to duckweed terminal taxa are much longer relative to other ingroup taxa (including Pistia), evidently as a result of higher rates of nucleotide substitutions and insertion/deletion events. Morphological reduction within the duckweeds roughly correlates with accelerated chloroplast genome evolution.     

Cobbania corrugata gen. et comb. nov. (Araceae): a floating aquatic monocot from the Upper Cretaceous of western North America

The fossil record of aquatic flowering plants broadens our understanding of their former diversity and origins from terrestrial ancestors. This paper describes a floating aquatic monocot from 71 whole plants and several isolated leaf fragments from Upper Cretaceous oxbow lake sediments in the Dinosaur Park Formation, Alberta, Canada. The new material is represented by rosettes of leaves and roots attached to short stems that are interconnected by stolons and corresponds to the fossil aroid originally described as Pistia corrugata Lesquereux. Up to six plants have been found interconnected on a single slab suggesting that these plants grew in extensive floating mats covering lakes and calm stretches of rivers. Stems have up to six leaves and large numbers of branched aquatic roots. The leaf is trumpet-shaped with an elongate clasping petiole, large aerenchymatous base, and a nearly circular blade rim. Leaf bases are often filled with sediment giving the leaf the appearance of having a basal pouch. Petioles have 6-9 veins that divide into an upper and lower set, and veins converge at an apical notch. A submarginal collective vein and at least two marginal veins with branching veins form the leaf rim. A series of dichotomizing and anastomosing veins characterize the adaxial leaf surface. Tertiary and quaternary veins form polygonal areolae. Leaf surfaces are covered in trichomes that, like those in Pistia stratiotes, probably aided in buoyancy. A reconstruction of the plant is presented. Based on unique leaf morphology, these fossil plants are clearly not assignable to the genus Pistia and are described as Cobbania corrugata (Lesquereux) Stockey, Rothwell et Johnson gen. et comb. nov. Recent systematic analyses using molecular characters resolve two separate origins of floating aquatic aroids included in the duckweeds and the genus Pistia. This new fossil genus increases our understanding of colonization of aquatic habitats by revealing a third possible origin of the floating aquatic habit within Araceae.     

EVOLUTIONARY AND ECOLOGICAL SIGNIFICANCE OF STARCH STORAGE IN POLLEN OF THE ARACEAE

Starch content was qualitatively assessed for pollen of 79 of the 111 currently recognized genera of the family Araceae—one of three monocot families known to exhibit both starchy and starchless pollen. Although 73% of the genera investigated had exclusively starchy pollen, character correlation suggests that starchless pollen is the primitive type for the family Araceae, as well as for monocots in general. Pollen starch content is a highly conservative character at the generic level in Araceae; only a single genus (Schismatoglottis) clearly exhibits both character states. The distribution of starchy pollen among aroid genera is consistent with what have here been termed Bakers' Starch Laws. Aroid pollen below a certain critical diameter—17-25 μm—is almost invariably starchless. Larger pollen is nearly always starchy, except where insect pollinators may use pollen nutritionally. There is strong evidence that the trend from starchless to starchy pollen in Araceae is reversible, according to the constraints imposed by the aforementioned factors.     

Biogeography of the Pistia clade (Araceae): based on chloroplast and mitochondrial DNA sequences and Bayesian divergence time inference

Pistia stratiotes (water lettuce) and Lemna (duckweeds) are the only free-floating aquatic Araceae. The geographic origin and phylogenetic placement of these unrelated aroids present long-standing problems because of their highly modified reproductive structures and wide geographical distributions. We sampled chloroplast (trnL-trnF and rpl20-rps12 spacers, trnL intron) and mitochondrial sequences (nad1 b/c intron) for all genera implicated as close relatives of Pistia by morphological, restriction site, and sequencing data, and present a hypothesis about its geographic origin based on the consensus of trees obtained from the combined data, using Bayesian, maximum likelihood, parsimony, and distance analyses. Of the 14 genera closest to Pistia, only Alocasia, Arisaema, and Typhonium are species-rich, and the latter two were studied previously, facilitating the choice of representatives that span the roots of these genera. Results indicate that Pistia and the Seychelles endemic Protarum sechellarum are the basalmost branches in a grade comprising the tribes Colocasieae (Ariopsis, Steudnera, Remusatia, Alocasia, Colocasia), Arisaemateae (Arisaema, Pinellia), and Areae (Arum, Biarum, Dracunculus, Eminium, Helicodiceros, Theriophonum, Typhonium). Unexpectedly, all Areae genera are embedded in Typhonium, which throws new light on the geographic history of Areae. A Bayesian analysis of divergence times that explores the effects of multiple fossil and geological calibration points indicates that the Pistia lineage is 90 to 76 million years (my) old. The oldest fossils of the Pistia clade, though not Pistia itself, are 45-my-old leaves from Germany; the closest outgroup, Peltandreae (comprising a few species in Florida, the Mediterranean, and Madagascar), is known from 60-my-old leaves from Europe, Kazakhstan, North Dakota, and Tennessee. Based on the geographic ranges of close relatives, Pistia likely originated in the Tethys region, with Protarum then surviving on the Seychelles, which became isolated from Madagascar and India in the Late Cretaceous (85 my ago). Pistia and Protarum provide striking examples of ancient lineages that appear to have survived in unique or isolated habitats.     

Phylogenetic relationships of aroids and duckweeds (Araceae) inferred from coding and noncoding plastid DNA

Familial, subfamilial, and tribal monophyly and relationships of aroids and duckweeds were assessed by parsimony and Bayesian phylogenetic analyses of five regions of coding (rbcL, matK) and noncoding plastid DNA (partial trnK intron, trnL intron, trnL-trnF spacer) for exemplars of nearly all aroid and duckweed genera. Our analyses confirm the position of Lemna and its allies (formerly Lemnaceae) within Araceae as the well-supported sister group of all aroids except Gymnostachydoideae and Orontioideae. The last two subfamilies form the sister clade of the rest of the family. Monophyly of subfamilies Orontioideae, Pothoideae, Monsteroideae, and Lasioideae is supported, but Aroideae are paraphyletic if Calla is maintained in its own subfamily (Calloideae). Our results suggest expansion of the recently proposed subfamily Zamioculcadoideae (Zamioculcas, Gonatopus) to include Stylochaeton and identify problems in the current delimitation of tribes Anadendreae, Heteropsideae, and Monstereae (Monsteroideae), Caladieae/Zomicarpeae, and Colocasieae (Aroideae). Canalization of traits of the spathe and spadix considered typical of Araceae evolved after the split of Gymnostachydoideae, Orontioideae, and Lemnoideae. An association with aquatic habitats is a plesiomorphic attribute in Araceae, occurring in the helophytic Orontioideae and free-floating Lemnoideae, but evolving independently in various derived aroid lineages including free-floating Pistia (Aroideae).     

Effect of Cadmium on the Level of Isoprenoid-Derived Phytohormones in Duckweed Wolffia arrhiza

Journal of Plant Growth Regulation - Wolffia arrhiza (L.) Horkel ex Wimm. is an aquatic plant belonging to the Lemnaceae family. It does not have leaves, stems, and roots, flowers rarely occur,...     

Pollen Morphology in Tribe Lactuceae (Compositae)

The Lactuceae contain two basic pollen types, echinolophate and echinate. Most taxa have echinolophate, tricolporate pollen. Internally, most ektexines are composed of a perforate spiny tectum, several levels of columellae, a cavus, and a foot layer. In lacunae, the columellae are reduced to a single level and the cavus is often absent. Highly modified echinolophate pollen grains are found in Scolymus, Scorzonera and Tragopogon. Scolymus, Catananche, Scorzonera, and Tolpis have distinctive exine stratification patterns. Exines of Catananche and, to a lesser extent, those of Tragopogon contain internal foramina like those found in the Heliantheae. Echinate pollen is found in all subtribes and is probably ancestral. However, some echinate grains are probably derived.     

Fossil Araceae from a Paleocene neotropical rainforest in Colombia

Both the fossil record and molecular data support a long evolutionary history for the Araceae. Although the family is diverse in tropical America today, most araceous fossils, however, have been recorded from middle and high latitudes. Here, we report fossil leaves of Araceae from the middle-late Paleocene of northern Colombia, and review fossil araceous pollen grains from the same interval. Two of the fossil leaf species are placed in the new fossil morphogenus Petrocardium Herrera, Jaramillo, Dilcher, Wing et Gomez-N gen. nov.; these fossils are very similar in leaf morphology to extant Anthurium; however, their relationship to the genus is still unresolved. A third fossil leaf type from Cerrejón is recognized as a species of the extant genus Montrichardia, the first fossil record for this genus. These fossils inhabited a coastal rainforest ～60-58 million years ago with broadly similar habitat preferences to modern Araceae.     

Reasons and consequences of the lack of a sporopollenin ektexine in Aroideae (Araceae)

The ultrastructure of pollen walls in Araceae is characterized by the absence of a stable sporopollenin outer exine layer in subfamily Aroideae, and by the presence of several distinctive pollen characters typical for the other aroid subfamilies. This article discusses if and to which extent such distinctive pollen characters are mirrored in various classifications of Araceae, basing either on morphological or on molecular data. Accordingly, the pollen characters perfectly reflect the actual subfamily classification, and also recent arrangements of clades in trees basing on molecular data. The actual subfamilies appear no longer eurypalynous, but now strictly stenopalynous. Aside from the (settled) classification problem the fundamental question is addressed why do Aroideae lack an elaborated sporopollenin ektexine. Possible pollination biology benefits, deriving from an absence of an elaborated sporopollenin ektexine in Aroideae, are presented and discussed. Compared with all other subfamilies the most advanced and by far largest subfamily Aroideae has lost several crucial characters and simultaneously acquired corresponding opposed characters, amongst others a non-sporopollenin exine layer and an unusual thick and spongy endexine. Taken together, losses and acquisitions are interpreted as a major paradigm shift in Araceae evolution, which took place according to the fossil record probably in the Paleogene.     

Studies on Pollen Morphology of Podocarpaceae from China

The pollen morphology and ultrastructure of exine of Podocarpaceae in China were examined with light microscope, scanning electron microscope and transmission electron microscope. The pollen grains of Podocarpus have rather large and prominent sacs on both sides of body, and are 53.9-74.8 μm long in total, with their bodies 29.6-45.2 μm long and 19.1-31.3 μm wide. The sacs are smooth on outer surface with perforation, but reticulate inside. On distal view, they are obviously of radial muri from its base. The body is oblate or spheroidal, laddershaped on distal face. The exine of the capis tuberculate, but more distinctly on the margin than in the centre. The pollen grains of Dacrydium are of small and indistinct sacs around body, which are composed of many small bladders. The body is subcircular in outline. Both body and sacs are irrugulate tuberculate under SEM. Examination of thin sections of Podocarpus macrophyllus var. maki with TEM reveals that the exine includes ectexine and endexine. It is interesting to note that foot layer of ectexine possesses lamellar stru cture, but endexine is homogeneous in structure and lighter in colour. This character is specific in the gymnosperms. Based on informations of fossil pollen grains, Podocarpaceae is rather primitive and of ancient origin.     

Pollen Morphology of Tundra Shrubs and Submarginal Plants from Barrow, Alaska

Investigation of plant morphological features, pollen, and habitat have been made for two shrub species from Barrow, Alaska, namely Dryas integrifoila M. Vahl and Salix rotundifolia Trautv., both of which are endemic to the Arctic floristic area. The former species has small lanceolate or plate leaves, whereas the latter has rounded leaves with distinct veins, rich in vitamin C. Both have dwarf and sprawling habits. Pollen studies showed that the pollen grains of the two species are spheroidal to sub-spheroidal or prolate. The type of aperture was tricolporate; pollen size 26.3-31.3 μm; ornamentation finely reticulate under a light microscope （LM） and strlate-reticulate under a scanning electron microscope （SEM） for D. integrafoila and finely reticulate under the LM and SEM for S. rotundifolia. Comparisons were made between the pollen from the same species from Arctic collections with those from China and Japan. Investigation of pollen morphology of tundra plants can provide significant data for comparative studies of fossil pollen and for the reconstruction of paleovegetation and paleoclimate in the Barrow area.     

中国天南星科花粉形态的研究

利用扫描电镜对天南星科Araceae22属28种(除Arum maculatum产自德国外,其余均产自中国) 及菖蒲科Acoraceae 1属2种植物的花粉形态进行了观察。结果显示天南星科花粉形态在科内变异很 大。花粉粒形状从球形、近球形、椭球形到扁球形和橄榄形;萌发孔类型有散孔型、具薄壁区型、环沟型 或无萌发孔;外壁纹饰为小穴状、网状、肋条状、条纹状、疣状、具刺或光滑。主要依据花粉形态方面的证 据探讨了崖角藤属Rhaphidophora、麒麟叶属Epipremnam 、龟背竹属Monstera 3属的属间关系以及犁头尖属Typhonium属下分类中存在的一些问题。     

Study on the Decomposition of Pistia stratiotes L. (Araceae) in Cisne Reservoir,Uruguay

A study on the decomposition process of Pistia stratiotes L. was carried out in Cisne Reservoir, Uruguay. For this purpose, leaves and roots were considered separately, and the process was studied in the littoral and the pelagic zone. The litter bag technique was used to estimate dry weight losses at different times. Leaves decomposed faster than roots in both zones. Pistia decomposed faster in the pelagic zone due to better oxygen conditions and a more intensive water movement that removes material from within the bags. Phosphorus, potassium, sodium and magnesium were leached rapidly during the first week. Nitrogen content in the leaves initially increased, reaching its maximum in the littoral zone that coincided with that of bacterial numbers colonizing the litter. The number of macroinvertebrates, dominated by Chironomidae, was low. A rough estimation of the phosphorus impact on the littoral zone associated to the decomposition process shows that after 24 h between 13.9 and 16.8 μg-at.1⁻¹ have been released to the water.     

Ammonium and nitrate uptake by the floating plant Landoltia punctata

BACKGROUND AND AIMS: Plants from the family Lemnaceae are widely used in ecological engineering projects to purify wastewater and eutrophic water bodies. However, the biology of nutrient uptake mechanisms in plants of this family is still poorly understood. There is controversy over whether Lemnaceae roots are involved in nutrient uptake. No information is available on nitrogen (N) preferences and capacity of Landoltia punctata (dotted duckweed), one of the best prospective species in Lemnaceae for phytomelioration and biomass production. The aim of this study was to assess L. punctata plants for their ability to take up NH4+ and NO3- by both roots and fronds. METHODS: NO3- and NH4+ fluxes were estimated by a non-invasive ion-selective microelectrode technique. This technique allows direct measurements of ion fluxes across the root or frond surface of an intact plant. KEY RESULTS: Landoltia punctata plants took up NH4+ and NO3- by both fronds and roots. Spatial distribution of NH4+ and NO3- fluxes demonstrated that, although ion fluxes at the most distal parts of the root were uneven, the mature part of the root was involved in N uptake. Despite the absolute flux values for NH4+ and NO3- being lower in roots than at the frond surface, the overall capacity of roots to take up ions was similar to that of fronds because the surface area of roots was larger. L. punctata plants preferred to take up NH4+ over NO3- when both N sources were available. CONCLUSIONS: Landoltia punctata plants take up nitrogen by both roots and fronds. When both sources of N are available, plants prefer to take up NH4+, but will take up NO3- when it is the only N source.     

A Study on Pollen Morphology of Eucommia ulmoides Oliver

Eucommia ulmoides Oliver is endemic to China. The pollen morphology and exine ultrastructure were examined under LM, SEM and TEM. Pollen grains are prolate, polar axis 30.5-54.8 μm long, with the average 32.7 μm, equatorial axis 27.8-31.3 μm long, with the average 29.2 μm, tricolporoidate, but sometimes the outline of ora could be observed and elliptic in shape. Colpi are narrow, uequal in length, often two long and one short or two short and one long, sometimes rather irregularly arranged, with indistinct and thin colpus membrance. Exine psilate under LM, granulate under SEM, and shortly baculate under TEM. Tectum is thin with dense and small granules, columellae layer consists of short bacules, and foot layer very thick. Some taxonomists (Cronquist, 1968) consider that Eucommiaceae is related to Hamamelidales, but others (Takhtajan, 1969) to Urticales. The Urticales is of the porate type of pollen grains, while Eucommiaceae of tricolporoidate type, and thus the former is more advanced than the latter. Pollen grains of some members of Hamamelidales, tricolporoidate, are similar to those of Eucommiaceae. We therefore consider that Eucommiaceae is related to Hama-melidales.     

Aquatic adventitious roots of the wetland plant Meionectes brownii can photosynthesize: implications for root function during flooding

? Many wetland plants produce aquatic adventitious roots from submerged stems. Aquatic roots can form chloroplasts, potentially producing endogenous carbon and oxygen. Here, aquatic root photosynthesis was evaluated in the wetland plant Meionectes brownii, which grows extensive stem-borne aquatic roots during submergence. ? Underwater photosynthetic light and CO(2) response curves were determined for aquatic-adapted leaves, stems and aquatic roots of M. brownii. Oxygen microelectrode and (14)CO(2)-uptake experiments determined shoot inputs of O(2) and photosynthate into aquatic roots. ? Aquatic adventitious roots contain a complete photosynthetic pathway. Underwater photosynthetic rates are similar to those of stems, with a maximum net photosynthetic rate (P(max)) of 0.38 μmol O(2) m(-2) s(-1); however, this is c. 30-fold lower than that of aquatic-adapted leaves. Under saturating light with 300 mmol m(-3) dissolved CO(2), aquatic roots fix carbon at 0.016 μmol CO(2) g(-1) DM s(-1). Illuminated aquatic roots do not rely on exogenous inputs of O(2). ? The photosynthetic ability of aquatic roots presumably offers an advantage to submerged M. brownii as aquatic roots, unlike sediment roots, need little O(2) and carbohydrate inputs from the shoot when illuminated.     

第四纪地层中常见的菊科植物花粉及其起源与分布

文中描述近年来在不同地区第四纪地层中发现的20多种类型菊科植物花粉形态特征,主要有3大类型:外壁具刺型、外壁内部具基柱型和大网胞型。并对它们的植物亲缘关系进行分类探讨。这些类型的化石花粉的植物关系都可归属到相应的现代菊科植物的族或属。据记载,早始新世古地中海至美国西北部亚热带略干旱温暖环境中出现的菊科祖先,可能是菊科植物的起源中心。根据现代植物属(或族)的相关资料,文中讨论了主要类型花粉的起源或分布。绝大多数类型分布于欧亚大陆及北美,在亚洲主要集中于喜马拉雅山及中国西南部。     

Global history of the ancient monocot family Araceae inferred with models accounting for past continental positions and previous ranges based on fossils

? The family Araceae (3790 species, 117 genera) has one of the oldest fossil records among angiosperms. Ecologically, members of this family range from free-floating aquatics (Pistia and Lemna) to tropical epiphytes. Here, we infer some of the macroevolutionary processes that have led to the worldwide range of this family and test how the inclusion of fossil (formerly occupied) geographical ranges affects biogeographical reconstructions. ? Using a complete genus-level phylogeny from plastid sequences and outgroups representing the 13 other Alismatales families, we estimate divergence times by applying different clock models and reconstruct range shifts under different models of past continental connectivity, with or without the incorporation of fossil locations. ? Araceae began to diversify in the Early Cretaceous (when the breakup of Pangea was in its final stages), and all eight subfamilies existed before the K/T boundary. Early lineages persist in Laurasia, with several relatively recent entries into Africa, South America, South-East Asia and Australia. ? Water-associated habitats appear to be ancestral in the family, and DNA substitution rates are especially high in free-floating Araceae. Past distributions inferred when fossils are included differ in nontrivial ways from those without fossils. Our complete genus-level time-scale for the Araceae may prove to be useful for ecological and physiological studies.