Dicot Families Research Articles

Systematics and phytogeography of selected Eocene Okanagan Highlands plants

The diverse Early to Middle Eocene Okanagan Highlands floras of south central British Columbia and northeastern Washington reflect a time of rapid evolution and the early radiation of many dicot families that are currently significant elements of temperate floras. Recent studies of the Republic, Washington flora (Klondike Mountain Formation) and related Okanagan floras in British Columbia have documented both the earliest, and sometimes the only, known fossil occurrences of genera. Today many once more widespread taxa are restricted, particularly to Asian and (or) eastern North American refugia. Examples include members of the families Betulaceae (birch, hazelnut), Rosaceae (rose), Hamamelidaceae (witch hazel), and the endemic Asian family Trochodendraceae. Earliest occurrences are noted for Neviusia (Rosaceae), Trochodendron (Trochodendraceae), Corylus and Carpinus (both Betulaceae). The first unequivocal leaf records of Corylopsis and Fothergilla (both Hamamelidaceae), and two new Eocene species of the extinct fruit Palaeocarpinus (Betulaceae) are also recognized. Today, Trochodendron and Corylopsis are restricted to Asia, whereas Neviusia and Fothergilla, genera with close Asian relatives, occur only in North America. Corylus johnsonii from Republic is most similar to the extant Asian species C. heterophylla, C. wangii, and C. ferox. Neviusia leaves from One Mile Creek near Princeton, British Columbia are more similar to N. cliftonii, an endemic from Mount Shasta, California, than to N. alabamensis of southeastern North America. A better documentation of the Okanagan Highlands floras is essential to our understanding of the evolution of North American temperate floras and the nature of Asian – North American disjunct taxa.

CDNA cloning and characterization of a ribosome inactivating protein of a hemi-parasitic plant ( Viscum album L.) from North-Western Himalaya (India)

Mistletoe ribosome inactivating proteins (RIPs) are excellent immunomodulators obtained from a hemi-parasitic plant Viscum album L. In the present study, we have characterized and cloned a 65 kDa heterodimeric RIP from Himalayan V. album. Himalayan mistletoe ribosome inactivating protein (HmRIP) possessed unique sugar affinity for l-Rhamnose, Meso-inositol and l-Arabinose besides Galactose and N-acetyl-Galactosamine. The lectin activity was stable to a broad range of temperature (4–65 °C) and pH (2.5–12.5). cDNA cloning showed that HmRIP is 500 amino acids long and shortest among mistletoe RIPs. Amino acid sequence analyses revealed important differences at the functionally significant sites. In the lectin subunit, two critical residues forming base of the 2γ sugar-binding cleft were deleted. Such differences lead to a different conformation of sugar-binding cleft giving rise to unique sugar-binding properties of HmRIP. Toxin subunit also showed a sizeable deletion of four residue segment in the antigenic epitope (83–103) determining its antigenecity. Due to striking differences at the functional sites associated with medicinal properties, HmRIP is a novel type II RIP. In the phylogenetic tree based on amino acid sequence of type II RIPs from six dicot families, mistletoe RIPs branched out from the RIPs of all other taxa and formed a distinct and distant group supporting independent evolution of Viscaceae among the angiosperms.

Myco-heterotroph-fungus marriages - is fidelity over-rated?

Myco-heterotroph-fungus marriages - is fidelity over-rated?

Turnip mosaic virusand the quest for durable resistance

Summary Taxonomy: Turnip mosaic virus (TuMV) is a member of the genus Potyvirus (type species Potato virus Y) in the family Potyviridae. To date, TuMV is the only potyvirus known to infect brassicas. There are potyvirus isolates that appear serologically similar to TuMV when tested with polyclonal antisera that do not readily infect brassicas (Lesemann and Vetten, 1985). Physical properties: Virions are approximately 720 x 15-20 nm flexuous rods (Fig. 1) and are composed of 95% coat protein (CP) and 5% RNA. Hosts: TuMV has been isolated from a wide range of crop and weed plant species. It is known to infect at least 318 species in over 43 dicot families, including Cruciferae, Compositae, Chenopodiaceae, Leguminosae and Caryophyllaceae and is also known to infect monocots. It has the broadest known host range in terms of plant genera and families of any potyvirus. Aphid transmitted in the non-persistent manner, by at least 89 species, including Myzus persicae and Brevicoryne brassicae. Useful website: http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/57010072.htm.

Evolutionary relationships among self-incompatibility RNases.

T2-type RNases are responsible for self-pollen recognition and rejection in three distantly related families of flowering plants-the Solanaceae, Scrophulariaceae, and Rosaceae. We used phylogenetic analyses of 67 T2-type RNases together with information on intron number and position to determine whether the use of RNases for self-incompatibility in these families is homologous or convergent. All methods of phylogenetic reconstruction as well as patterns of variation in intron structure find that all self-incompatibility RNases along with non-S genes from only two taxa form a monophyletic clade. Several lines of evidence suggest that the best interpretation of this pattern is homology of self-incompatibility RNases from the Scrophulariaceae, Solanaceae, and Rosaceae. Because the most recent common ancestor of these three families is the ancestor of approximately 75% of dicot families, our results indicate that RNase-based self-incompatibility was the ancestral state in the majority of dicots.

Comparative pollen morphology and ultrastructure of the Callitrichaceae

The Callitrichaceae are an aquatic family of dicots that include the single, geographically cosmopolitan genus Callitriche. Callitriche contains 40-50 terrestrial, amphibious, and obligately submersed species, and it is the only known genus in the plant kingdom with co-occurring aerial and hydrophilous pollination syndromes. Pollen morphology and ultrastructure were described for 13 Callitriche species using scanning electron and transmission electron microscopy. Representative taxa of each growth form were examined; these included three terrestrial species (C. deflexa, C. peploides, and C. nuttallii), nine amphibious species (C. brutia, C. cophocarpa, C. cophocarpa-stagnalis hybrid, C. cribrosa, C. hamulata, C. heterophylla var. heterophylla, C. lusitanica, C. marginata, and C. trochlearis), and one obligately submersed species (C. truncata). Of the amphibious taxa, C. heterophylla var. heterophylla and C. trochlearis had internal geitonogamy, a type of internal self-fertilization. Pollen from all taxa was spheroidal, small, intectate, and lacked well-defined apertures. Taxa primarily differed with respect to exine thickness, surface ornamentation, and the presence or absence of aperture-like regions. The pollen of terrestrial species, as well as that of C. marginata, had well-developed exines with thick sculptured and basal layers. In general, amphibious taxa produced pollen with distinct, but thinner, exines than that of terrestrial taxa. Pollen of the amphibious taxa with internal geitonogamy had a thicker basal layer than species without internal geitonogamy, whereas the overall exine was reduced in C. hamulata and absent in C. brutia and C. lusitanica. Pollen of the obligately submersed C. truncata also lacked an exine. These palynological data were correlated with growth habits and related pollination biologies, as well as with phylogenetic interpretations of Callitrichaceae. Exine reduction or loss has evolved at least twice in the family, and it is associated with aneuploid reduction in chromosome number.

Plant invertase inhibitors: expression in cell culture and during plant development

This paper originates from a presentation at the International Conference on Assimilate Transport and Partitioning, Newcastle, NSW, August 1999. We have recently cloned cDNAs encoding two invertase inhibitors from Nicotiana tabacum, Nt-inh1, an apoplastic isoform, and Nt-inhh, a vacuolar isoform (Greiner et al. (1998) Plant Phys. 116, 733–742; Greiner et al. (1999) Nature/Biotech. 17, 708–711). A database search revealed the presence of related sequences in other dicot families. Here we report the presence of Nt-inh1-related proteins (INH-RPs) in apoplastic fractions from Chenopodium rubrum and Daucus carota suspension-culture cells. Furthermore, we demonstrate that, in Lycopersicon esculentum, the expression of INH-RPs is highly regulated during plant development. In immature tomato fruits two INH-RP isoforms are expressed, whereas in mature fruit a single isoform is detected. Sequential extraction of apoplastic and intracellular fractions from mature fruit pericarp tissue revealed that the major portion of invertase and INH-RP are localized in the vacuole. Recovery of the non-glycosylated INH-RP with the glycosylated invertase from the Concanavalin A-bound fraction indicates that INH-RP forms a stable complex with vacuolar invertase. As Nt-inh1 and INH-RP from different species contain four conserved cysteine residues, we have compared the inhibitory activity of oxidized and dithiothreitol (DTT)-treated recombinant Nt-inh1 protein. Only the oxidized form is active as an invertase inhibitor. Its higher mobility during sodium dodecyl sulfate–gel electrophoresis, as compared to DTT-treated Nt-inh1, suggests that disulfide bridge(s) prevent the inhibitor from unfolding. A mechanism is proposed for the post-translational inactivation of cell wall and vacuolar invertases via invertase inhibitors during critical stages of plant development.

Weed Hosts of Soybean Cyst Nematode (Heterodera glycines) in Ohio1

Abstract: In greenhouse experiments, Ohio accessions of 22 weed species representing 13 dicot families were screened as alternative hosts of soybean cyst nematode (SCN, Heterodera glycines). Purple deadnettle (Lamium purpureum), henbit (Lamium amplexicaule), field pennycress (Thlaspi arvense), shepherd's-purse (Capsella bursa-pastoris), and a susceptible soybean (Glycine max) cultivar produced SCN population densities of 510, 155, 73, 1, and 366 cysts/450 cm3 soil, respectively, 5 wk after inoculation with eggs from a race 3 SCN population. Purple deadnettle was also a strong host of race 1 SCN and a weak host of race 6 SCN. Average numbers of eggs/cyst among race 3 hosts were highest in purple deadnettle (357), followed by soybean (292), field pennycress (266), henbit (122), and shepherd's-purse (none detected). To our knowledge, henbit is the only SCN host identified here that has been previously identified as a host. The weeds identified as SCN hosts in this study have a winter annual life cycle in Ohi...

A Comparative Study of Spacer Plasticity in Erect and Stoloniferous Herbs

Closely related plant species from a number of genera produce either erect (orthotropic) or creeping (plagiotropic) shoots. As a result, corresponding (homologous) organs, such as internodes or petioles, are oriented differently in space. They thus fulfil different functions; the elongation of vertically oriented structures shifts leaf blades into higher regions within the canopy, whereas the elongation of horizontally oriented structures does not. As a consequence, different degrees of internode or petiole plasticity may have evolved in erect and stoloniferous species to adjust the architecture of plants in case they are shaded. This study aims at testing the hypothesis that vertically oriented spacers have higher degrees of shade-induced plasticity in their length than horizontally oriented spacers. It is further hypothesized that a high degree of plasticity in spacer length involves costs in terms of increased biomass investment into elongating organs. These hypotheses were tested with nine herbaceous species pairs (each consisting of one erect and one closely related stoloniferous species) belonging to six different families of dicots. Vertical spacers had higher degrees of shade-induced plasticity than horizontal spacers. This was true for internodes and petioles of individual species and also for functionally corresponding (i.e. analogous) spacers within species pairs. In addition, plastic increases in spacer length were positively related to increased spacer weight and to increased biomass allocation to spacers under shaded conditions. These results show that spacer plasticity depends primarily on the function of spacers and not on the phylogenetic relations of the species. They also suggest that there are costs of plasticity in terms of biomass investment into elongating organs. Differences in the balance between costs and benefits of plasticity between vertical and horizontal spacers may have led to the evolution of high degrees of plasticity of vertically oriented spacers and low degrees of plasticity of horizontally oriented spacers, as observed in this study.

Pollination systems in the Asclepiadaceae: a survey and preliminary analysis

Using published and unpublished records of pollination in the dicot family Asclepiadaceae (the ‘milkweeds’) we offer a preliminary analysis of present-day pollination systems in the family. Variation in principal pollinators is apparent at and below the tribal level. The tribes Marsdenieae and Stapelieae and Asclepiadeae subtribe Gonolobineae are primarily Diptera-pollinated, a tentative conclusion also for the tribe Periploceae, and we emphasize the ubiquity and importance of fly pollination in the family. The rest of the tribe Asclepiadeae is pollinated in the main by Hymenoptera and Lepidoptera. Lack of data makes it impossible to draw even initial conclusions for the remaining tribes, Secamoneae and Fockeeae. Within the Asclepiadeae, there has been a trend towards more diverse pollination systems (incorporating butterflies and wasps) in the New World compared to the Old World. In terms of the taxonomic breadth of pollinators of individual species, Stapelieae is the most specialized tribe. We emphasize that this is only a preliminary account of pollination in the Asclepiadaceae, and detail areas where further work is urgently required.

Pollination systems in the Asclepiadaceae: a survey and preliminary analysis

Using published and unpublished records of pollination in the dicot family Asclepiadaceae (the ‘milkweeds’) we offer a preliminary analysis of present-day pollination systems in the family. Variation in principal pollinators is apparent at and below the tribal level. The tribes Marsdenieae and Stapelieae and Asclepiadeae subtribe Gonolobineae are primarily Diptera-pollinated, a tentative conclusion also for the tribe Periploceae, and we emphasize the ubiquity and importance of fly pollination in the family. The rest of the tribe Asclepiadeae is pollinated in the main by Hymenoptera and Lepidoptera. Lack of data makes it impossible to draw even initial conclusions for the remaining tribes, Secamoneae and Fockeeae. Within the Asclepiadeae, there has been a trend towards more diverse pollination systems (incorporating butterflies and wasps) in the New World compared to the Old World. In terms of the taxonomic breadth of pollinators of individual species, Stapelieae is the most specialized tribe. We emphasize that this is only a preliminary account of pollination in the Asclepiadaceae, and detail areas where further work is urgently required.

Self‐incompatibility RNases from three plant families: homology or convergence?

In the Rosaceae, Scrophulariaceae, and Solanaceae, the stylar product of the self-incompatibility (S-) locus is an RNase. Using protein sequence data from 34 RNase genes (three fungal RNases, seven angiosperm non-S RNases, 11 Rosaceae S-alleles, three Scrophulariaceae S-alleles, and ten Solanaceae S-alleles) we reconstructed the genealogy of angiosperm RNases using the neighbor joining method and two distance metrics in order to assess whether use of S-RNases in these families is the result of homology or convergence. Four monophyletic groups of angiosperm RNases were found: the S-RNases of each of the three families and a group comprising most of the angiosperm non-S RNases. The S-RNases of the Scrophulariaceae and Solanaceae were found to be homologous but strong inference concerning the homology or convergence of S-RNases from the Rosaceae with those of the other families was not possible because of uncertain placement of both the root and two of the angiosperm non-S RNases. The most recent common ancestor of the Rosaceae and both the Scrophulariaceae and Solanaceae is shared by ~80% of dicot families. If the -RNases of the Rosaceae are homologous to those of the Scrophulariaceae and Solanaceae, then many other dicot families might be expected to share RNases as the mechanism of gametophytic self-incompatibility.

Phylogenetic relationships of Lecythidaceae: a cladistic analysis using rbcL sequence and morphological data

This study examined in detail the rbcL sequence and morphological support for subfamilial relationships and monophyly of Lecythidaceae. Initially we needed to establish relationships of Lecythidaceae among other dicot families. To complete this we examined 47 rbcL sequences of 25 families along with molecular observations from several large analyses of rbcL data. All analyses strongly support the monophyly of the asterid III grouping. This analysis revealed Lecythidaceae to be paraphyletic and indicated potential outgroup relationships with Sapotaceae. Once relationships had been evaluated using molecular data we then concentrated on analyzing separate and combined morphological and molecular databases. The topology of the morphological data set was similar to the rbcL sequence and combined data sets except for the positioning of Napoleonaeoideae, Grias, Gustavia, and Oubanguia. According to the combined results, Planchonioideae, Lecythidoideae. and Foetidioideae are monophyletic, whereas the subfamily Napoleonaeoideae are paraphyletic. Nested within Napolconaeoideae, we found Asteronthos forms a strongly supported clade with Oubanguia (Scytopetalaceae). Foetidia, the only genus of Foetidioideae, is sister to Planchonioideae, and this clade is sister to Lecythidoideae. The [(Planchonioideae, Foetidioideae) Lecythidoideae are sister to Asteranthos/Oubanguia. Napoleonaeoideae are sister to the rest of Lecythidaceae.

A Molecular Evaluation of the Monophyly of the Order Ebenales Based Upon rbcL Sequence Data

Molecular support for monophyly of Ebenales and its phylogenetic relationships to other dicot families was investigated using parsimony analysis of nucleotide sequences of the large subunit of ribulose-1,5-biphosphate carboxylase (rbcL). All families of Ebenales were examined except for the remote monogeneric family Lissocarpaceae, due to the lack of material. In addition we examined 93 rbcL sequences of 34 other families. All analyses strongly support monophyly of the asterid III grouping (identified in an analysis of 500 rbcL sequences by Chase et al.). The rbcL tree identified Ebenales to be distributed among several major subclades of the asterid III clade. Sapotaceae are sister to Symplocaceae and more closely related to Lecythidaceae/Scytopetalaceae than to other families of Ebenales. Ebenaceae are sister to Primulales. Styracaceae are polyphyletic, with Diapensiaceae and some Styracaceae sister to Polemoniaceae, and this clade is then sister to members of Clethraceae and Styrax. Although the phylogenetic hypothesis appears to be poorly resolved between groups, there is considerable support, as indicated by decay and jackknife support, for many of the inter-familial relationships. Evolutionary relationships of Ebenales (Takhtajan 1987; Cronquist 1981, 1988; Dahlgren 1989; Thorne 1992) have been based on the importance of a few key characters and the general criterion of overall similarity to indicate relationships. Additionally many of the families placed within Ebenales are themselves defined by a combination of characters, many of which are also used at higher taxonomic levels. Evidence of the complexity of this problem can be seen in the varied treatments within and the circumscription of Ebenales (Table 1). Ebenales usually consists of two to 5 families and about 2,000 species, chiefly of tropical and subtropical regions (Takhtajan 1987; Cronquist 1981, 1988; Dahlgren 1989; Thorne 1992). As treated in this paper, (sensu Cronquist 1981) Ebenales is composed of the families Ebenaceae, Lissocarpaceae, Sapotaceae, Styracaceae, and Symplocaceae. These five families share only the following morphological features: woodiness, simple leaves, radially symmetrical flowers, axile placentation, (1-8) tenuninucellate ovules per locule, and few large seeds with endosperm. Ebenales s.l. are thus characterized by a combination of features, none of which are individually unique to the order nor unusual among dicots in general. The families that make up the order vary from the morphologically distinctive monogeneric Lissocarpaceae and Symplocaceae to the highly variable Styracaceae and the large Ebenaceae and Sapotaceae. Concepts of evolutionary relationships among Ebenales are conflicting. Cronquist (1981, 1988) believed that Ebenales were derived from the thealean complex. Thorne (1992) and Dahlgren (1983, 1989) assigned Ebenaceae, Lissocarpaceae, Sapotaceae, and Styracaceae to Ebenales. Thorne placed Symplocaceae closer to Theales whereas Dahlgren considered Symplocaceae to belong within Cornales. Takhtajan's (1987) interpretation of relationships treated these five families in three different orders: Ebenaceae, Lissocarpaceae and Styracaceae in Ebenales; Sapotaceae in Sapotales; and Symplocaceae in Theales (Table 1). Wagenitz (1964) included Ebenaceae, Hoplestigmataceae, Lissocarpaceae, Sapotaceae, Sarcospermataceae, Styracaceae, and Symplocaceae in Ebenales. Hutchinson (1967, 1969, 1973) recognized two orders, Ebenales and Styracales. Ebenales contained Ebenaceae, Sapotaceae, and Sarcospermataceae (usually included in Sapotaceae). Styracales included Lissocarpaceae, Styracaceae, and Symplocaceae. Hutchinson believed that Ebenaceae provided a link between Myrsinaceae (Myrsinales) and Sapotaceae (Ebenales), suggesting that both orders probably were derived from thealean stock and stating that Styracales was difficult to place in any system. Nooteboom (1975) also believed, on the basis of

Types of carbohydrate reserves in pollen: localization, systematic distribution and ecophysiological significance

Dehiscing pollen grains of 901 species belonging to 104 dicot families and 15 monocot families were scored for starch reserves. Starch grains showed different physico-chemical properties i.e. colour after iodine - potassium iodide staining and birefringence or otherwise under polarized light. Further tests performed in a limited number of species revealed other kinds of carbohydrate reserves in the cytoplasm but outside plastids. From these observations, it results that carbohydrate reserves may be stored in plastids only (amyloplasts), in the cytoplasm but not in plastids, or in both. These kinds of pollen reserves are only partly in line with systematics, as only certain families consistently show the same type of reserve. These and previous findings suggest that the presence of polysaccharides in the cytoplasm prevents rapid decrease in viability due to desiccation. In this sense, our findings are in line with ecophysiological adaptations such as the respective pollination syndrome.

Multiple Independent Losses of Two Genes and One Intron from Legume Chloroplast Genomes

The losses of genes or introns from the chloroplast genome are of potential utility as phylogenetic characters. Previous broad surveys of angiosperms, along with sequencing studies in Pisum sativum, uncovered several instances of variation for such characters within the Legumi- nosae. Using a slot blot hybridization method that did not require high molecular weight DNA, probes for six genes and three introns typically found in angiosperm chloroplast genomes were used to screen 392 legume genera, representing all three subfamilies and 50 out of 51 tribes, and 48 genera from 26 other families of dicots. Few cases of chloroplast gene or intron loss from chloroplast genomes were observed among nonlegumes or within the legume subfamilies Mimo- soideae and Caesalpinioideae, but numerous apparent losses were observed in the large subfamily Papilionoideae. Certain cases of suspected losses were tested by polymerase chain reaction. The genes rpl2 and rbcL appear to be present in all taxa surveyed, and virtually all possess accD. In contrast, ORF184 and rpsl6 each appear to have been lost multiple, independent times within Leguminosae, while all members of the family appear to lack rp122. The intron of rpl2 has likely been lost at least four times within the family, and its absence is a synapomorphy for a core group of the papilionoid tribe Desmodieae. No convincing evidence of loss was observed among legumes for the introns of trnI and rpll6. These results indicate that gene or intron loss characters may often be homoplastic. Intron losses are a more reliable and valuable class of phylogenetic characters than are gene losses.

Angiosperm growth habit, dispersal and diversification reconsidered

Summary Previous studies have sought to elucidate the relationship between dispersal mode (biotic versus abiotic) and the taxonomic diversification of angiosperm families, but with ambiguous results. In this study, we propose the hypothesis that the combination of (1) the large seed size required of plants germinating in closed, lightpoor environments and (2) the necessity to move disseminules away from the maternal plant in order to avoid intraspecific competition, predation and pathogens should favour biotically-dispersed relative to abiotically-dispersed woody arborescent angiosperms, resulting in higher diversification of the former. In this paper, we seek patterns of diversification that support this hypothesis. We examine the association between dispersal mode, growth habit and taxonomic richness of monocotyledon and dicotyledon families using (1) contingency table analyses to detect the effect of dispersal mode on the relative abundances and diversification of woody versus herbaceous taxa and (2) non-parametric analyses of variance to detect the statistical effect of dispersal mode on taxonomic diversification (mean number of species per genus, genera per family and species per family) in monocot and dicot families dominated by biotic or abiotic dispersal. We found a clear statistical effect of dispersal mode on diversification. Among families of woody dicots, dispersal by vertebrates is associated with significantly higher levels of species per genus, genera per family and species per family than is abiotic dispersal. The same pattern is observed among woody monocots, but is not significant at the 0.05 level. Among families of herbaceous monocots and dicots, the situation is reversed, with abiotically-dispersed families exhibiting higher levels of diversification than vertebratedispersed families. When woody and herbaceous families are pooled, there is no association between dispersal mode and diversification. These data coincide with evidence from the fossil record to suggest vertebrate dispersal has positively contributed to the diversification of woody angiosperms. We suggest that vertebrate dispersal may have promoted the diversity of extant taxa by reducing the probability of extinction over evolutionary time, rather than by elevating speciation rates. Our results suggest vertebrate dispersal has contributed to, but does not explain in toto, the diversity of living angiosperms.

Relationships of Droseraceae: A Cladistic Analysis of rbcL Sequence and Morphological Data

Molecular support for the monophyly of Droseraceae and its phylogenetic relationships to other dicot families was investigated using parsimony analysis of nucleotide sequences of the large subunit of ribulose-1,5-bisphosphate carboxylase (rbcL). Analysis of 100 species of plants including families of subclasses Rosidae, Hamamelidae, Dilleniidae, and Caryophyllidae (sensu Cronquist) placed monophyletic Droseraceae in the same clade as Caryophyllidae and Nepenthaceae (Dilleniidae). In a second analysis of 14 species of Droseraceae, 15 caryophyllids, one Nepenthaceae, and three Santalales, a single most-parsimonious tree was found in which Droseraceae are monophyletic, although the position of Drosophyllum as a member of Droseraceae is only weakly supported. The rbcL tree identified four major lineages within genus Drosera: 1) Dionaea; 2) the regia-clade that contains only Drosera regia; 3) the capensis-clade that contains the South African and temperate species outside of Australia; and 4) the peltata-clade that consists of principally Australian endemics. A separate analysis of 14 morphological and phytochemical characters is in general agreement with the rbcL tree except for the placement of Nepenthes, Drosophyllum, and Drosera burmanni. A combined analysis of both data sets places Drosophyllum in a clade with Triphyophyllum (Dioncophyllaceae).

Relationships of Droseraceae: a cladistic analysis of rbcL sequence and morphological data

Molecular support for the monophyly of Droseraceae and its phylogenetic relationships to other dicot families was investigated using parsimony analysis of nucleotide sequences of the large subunit of ribulose‐1,5‐bisphosphate carboxylase (rbcL). Analysis of 100 species of plants including families of subclasses Rosidae, Hamamelidae, Dilleniidae, and Caryophyllidae (sensu Cronquist) placed monophyletic Droseraceae in the same clade as Caryophyllidae and Nepenthaceae (Dilleniidae). In a second analysis of 14 species of Droseraceae, 15 caryophyllids, one Nepenthaceae, and three Santalales, a single most‐parsimonious tree was found in which Droseraceae are monophyletic, although the position of Drosophyllum as a member of Droseraceae is only weakly supported. The rbcL tree identified four major lineages within genus Drosera: 1) Dionaea; 2) the regia‐clade that contains only Drosera regia; 3) the capensis‐clade that contains the South African and temperate species outside of Australia; and 4) the peltata‐clade that consists of principally Australian endemics. A separate analysis of 14 morphological and phytochemical characters is in general agreement with the rbcL tree except for the placement of Nepenthes, Drosophyllum, and Drosera burmanni. A combined analysis of both data sets places Drosophyllum in a clade with Triphyophyllum (Dioncophyllaceae).

Chromosome Numbers and Their Systematic Significance in Some Mexican Melastomataceae

Original meiotic chromosome counts are reported for 35 species and one natural interspecific hybrid in 11 genera of Mexican Melastomataceae. These include first counts for 24 species in three of the nine recognized New World tribes in the family. Counts of n = 18 for Arthrostemma parvifolium and n = 36 for Topobea calycularis represent new numbers for these genera. Other counts for species of Arthrostemma (n = 30), Centradenia (n = 18), Clidemia (n = 17, 23), Conostegia (n = 17), Heterocentron (n = 18), Leandra (n = 17), Miconia (n = 17), Monochaetum (n = 18), Pterolepis (n = 7), and Tibouchina (n = 9, 18) corroborate previously reported numbers for these genera. Centradenia, Heterocentron, and Monochaetum with n = 18 and Conostegia with n = 17 appear to have remarkably constant chromosome numbers, whereas Tibouchina exhibits a polyploid series based on x = 9. Clidemia, Leandra, and Miconia, the largest genera of Miconieae, show greatest variation in chromosome numbers. The widespread occurrence of n = 17 suggests that this is the base number in the Miconieae. Two hypotheses are presented to explain the origin of x = 17 in the Miconieae. One suggests straight autotetraploidization of x = 9 followed by chromosome loss (2x 1). The allotetraploid hypothesis proposes that x = 17 is of dibasic origin and may have formed by ancient hybridization of species with 7 and 10 or 8 and 9 haploid chromosomes. The Melastomataceae, a largely tropical family of dicots comprising 185-190 genera and approximately 5000 species, are the largest of the 13 core families in the Myrtales (Dahlgren and Thorne 1984). Unlike the Myrtaceae, the only other family in the order with over 3000 species, the Melastomataceae have been poorly known cytologically. As of 1967, a summary of published chromosome data for the melastomes listed numbers for 24 genera and 56 species (Bolkhovskikh et al. 1969). Only 10 of the numbers enumerated in that summary pertained to New World species. Subsequent papers containing chromosome information about New World melastomes consisted of scattered reports for selected species of Centradenia G. Don (Almeda 1977), Mecranium J. D. Hooker (Nevling 1969), Miconia Ruiz & Pavon (Nevling 1969), Monochaetum (DC.) Naudin (Almeda 1978), Pilocosta Almeda & Whiffin (Almeda and Whiffin 1981), Rhexia L. (Kral and Bostick 1969), Rhynchanthera DC. (Davidse 1970), and Tibouchina Aublet (Favarger 1962; Gadella et al. 1969). In a major review of chromosome cytology in the angiosperms, Raven (1975) included the Melastomataceae in his enumeration of the 16 families in greatest need of additional study. Since then, the number of neotropical melastome species for which there is basic chromosome information has increased considerably so that species belonging to 53 of the 107 New World genera have now been subjected to some kind of preliminary study. Much of this new information was presented by Solt and Wurdack (1980) who reported chromosome numbers for 58 genera and 260 species. In this study we provide 59 meiotic counts for selected species of Melastomataceae from Mexico. Chromosome numbers have heretofore been reported for only 11 species in six genera of Mexican melastomes. A geographic emphasis on Mexico represents a convenient starting point in our effort to augment chromosome data for neotropical Melastomataceae. Mexico, with 25 genera and 190 species of Melastomataceae (63 of which are endemic to the country) is the northernmost limit for familial diversity in the western hemisphere.