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Topic: Gnetales

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Gnetum

Welwitschiales

Species

Ephedrales

Gymnosperm

Angiosperm

Namibia

Gnetae

Gnetophyta

Ephedra

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	[No title]
		The three existing genera, usually spoken of as members of the Gnetales, differ from one another more than is consistent with their inclusion in a single family; we may therefore better express their diverse characters by regarding them as types of three separate families—(t) Ephedroideae, genus Ephedra; (2) Welwitschioideae, genus Welwitschia; (3) Gnetoideae, genus Gnetum.
		Our knowledge of the Gnetales leaves much to be desired, but such facts as we possess would seem to indicate that this group is of special importance as foreshadowing, more than any other Gymnosperms, the Angiospermous type.
		The Gnetales probably had a separate origin from the other Gymnosperms; they carry us nearer to the Angiosperms, but we have as yet no satisfactory evidence that they represent a stage in the direct line of Angiospermic evolution.
	encyclopedia.jrank.org /correction/edit?locale=en&content_id=28732 (2288 words)

	Cycadales
		If Gnetales and Pinales are sister taxa, the evolution of the inverted repeat would involve its expansion in the common ancestor of the two and its subsequent loss in Pinaceae.
		Although nearly all Pinales have an ovuliferous scale or modifications of this, Gnetales are distinctive in having strobili with decussating bracts (Magallón and Sanderson 2002).
		Wherever Gnetales are to be placed, they seem to be a very derived group; here they are kept on a separate page.
	www.mobot.org /MOBOT/research/APweb/orders/cycadales.html (3559 words)

	A New Gnetophyte from the Late Carnian
		But the notion that the Gnetales are closely related to angiosperms also cycled through a period of disfavor, only to reemerge due to new evidence favoring a very close relationship with angiosperms (Doyle and Donoghue, 1986a, 1992).
		The grouping of male spikes may be similar to that of the bracts in being arranged in a tight spiral, indicating that the characteristic synapomorphy for the Gnetales of opposite or whorled appendages is probably an advancement over the condition in stem gnetophytes (Doyle and Donoghue, 1986b).
		Unlike the Gnetales, retention of two or more ovules (or the potential for more than one ovule) and a shift from prefertilization to postfertilization development of the ovule resulted in additionai specializations in angiosperms: (1) interseminal (sterile) scales modified to form a pollen tube transmission tissue that connects stigma with ovules (Fig.
	bcornet.tripod.com /Cornet96/Archaestrobilus.htm (10638 words)

	Phylogeny and evolution
		The Gnetales is a relict group of seed plants with a divers but almost unstudied fossil record.
		During the years they have been associated with angiosperms or with conifers, but their morphology is hard to interpret and relationships with other seed plants have never been fully understood.
		The morphological diversity and phylogenetic history of the Gnetales will be investigated, using data from these fossils as well as molecular and morphological data from recent species.
	www.nrm.se /researchandcollections/palaeontology/palaeobotany/research/angiospermsandgnetales/phylogenyandevolution.4.5fdc727f10d795b1c6e80008177.html.printable (329 words)

	Botany 2004 - Abstract Search
		Despite marked dissimilarity in habitat and habit among these genera, most phylogenetic analyses indicate that the Gnetales is monophyletic.
		The phylogenetic position of the Gnetales among seed plants has received much attention in recent years.
		Although mature pollen grains are inaperturate, the exine is considerably thinner between the plicae, or within the furrows, which have a straight morphology.
	www.2004.botanyconference.org /engine/search/index.php?func=detail&aid=1010 (327 words)

	GNETALES - Online Information article about GNETALES
		The three existing genera, usually spoken of as members of the Gnetales, differ from one another more than is consistent with their inclusion in a single See also:
		Our knowledge of the Gnetales leaves much to be desired, but such facts as we possess would seem to indicate that this See also:
		branch of the Gymnosperms; but be that as it may, it is in the Gnetales more than in any other Gymnosperms that we find features which help us to obtain a dim prospect of the lines along which the Angiosperms may have been evolved.
	encyclopedia.jrank.org /GEO_GNU/GNETALES.html (3120 words)

	Gnetales
		Plant woody, evergreen; nicotinic acid metabolised to trigonelline; lignins rich in guaiacyl units; true roots present, xylem exarch; shoot apical merisetm complex; stem with ectophloic eustele, endodermis 0, xylem endarch; vascular tissue in t.s.
		PINALES + GNETALES: pollen tube unbranched, growing towards the ovule, gametes non-motile, released from the distal end of the tube, siphonogamy; germination epigeal.
		For the morphology of Gnetales in the context of that of fossil gymnosperms, see e.g.
	www.mobot.org /MOBOT/research/APweb/orders/gnetales.html (1158 words)

	Burleigh, J. Gordon and Sarah Mathews.* (Site not responding. Last check: 2007-09-10)
		Different molecular trees suggest that Gnetales are sister to Pinaceae, to conifers, or to all other seed plants.
		Bayesian and parsimony analyses strongly support the gnepine hyothesis, in which Gnetales and Pinaceae are sister taxa.
		Triplet likelihood ratio tests provide evidence that organellar sequences from Gnetales are evolving significantly faster than those from other seed plants, suggesting that bias toward the gnepine hypothesis might result from the very long branches to Gnetales.
	www.botany2002.org /section12/abstracts/241.shtml (339 words)

	HAYCRAFT, COURTNEY J.* AND JEFFREY S. CARMICHAEL. (Site not responding. Last check: 2007-09-10)
		Gnetales and angiosperms represent the only extant seed plant groups that possess bisexual reproductive structures.
		Many species of Gnetales consist of female plants which produce only ovule-bearing strobili and male plants with structurally bisexual strobili.
		Interestingly, the ovules formed on male strobili are reported to be nonfunctional, but this phenomenon is poorly understood.
	www.ou.edu /cas/botany-micro/bsa-abst/section2/abstracts/31.shtml (238 words)

	Projects and Research Opportunities
		The presence of double fertilization in Gnetales was first reported in Science, as was the later finding that the product of the second fertilization event in Gnetales is not an embryo-nourishing tissue, but rather, a supernumerary embryo.
		The hypothesis that double fertilization events may be homologous in Gnetales and angiosperms rests upon two key suppositions: first, that Gnetales are the closest living relatives of angiosperms and second, that double fertilization to produce an embryo and an endosperm in flowering plants is, in fact, a synapomorphy of angiosperms.
		Although the hypothesis that Gnetales are closely related to angiosperms has been well supported in phylogenetic analyses of seed plants during the last fifteen years, almost all recent molecular phylogenetic analyses have failed to detect an affinity between Gnetales and angiosperms.
	spot.colorado.edu /~friedmaw/projects/dipl.html (841 words)

	Seed plant phylogeny inferred from all three plant genomes: Monophyly of extant gymnosperms and origin of Gnetales from ...
		Gnetales as sister to angiosperms (13, 14), consistent with
		Remarkably, the conifers are not monophyletic, and the Gnetales
		(8) and Hickey and Taylor (9) that Gnetales are paraphyletic
	www.pnas.org /cgi/content/full/97/8/4086 (5169 words)

	University of North Dakota \| Biology Department
		My previous work has focused on the reproductive biology of the Gnetales (Ephedra, Gnetum, and Welwitschia), an intriguing group of gymnosperms that are closely related to flowering plants.
		Sexual reproduction in flowering plants occurs by a process of double fertilization in which one fertilization event forms an embryo and a second fertilization event produces endosperm, a polyploid embryo-nourishing tissue found only in angiosperms.
		In addition, the reduced nature of the sexually mature female gametophyte in Gnetum is a result of heterochrony and represents a paedomorphic effect.
	www.und.edu /dept/biology/carmichael.htm (593 words)

	CiteULike: Dating dispersal and radiation in the gymnosperm Gnetum (Gnetales)--clock calibration when outgroup ... (Site not responding. Last check: 2007-09-10)
		Because Gnetum has no fossil record, we relied on fossils from other Gnetales and from the seed plant lineages conifers, Ginkgo, cycads, and angiosperms to constrain a molecular clock and obtain absolute times for within-Gnetum divergence events.
		Relationships among Gnetales and the other seed plant lineages are still unresolved, and we therefore used differently resolved topologies, including one that contained a basal polytomy among gymnosperms.
		For a small set of Gnetales exemplars (n = 13) in which rbcL and matK satisfied the clock assumption, we also obtained time estimates from a strict clock, calibrated with one outgroup fossil.
	www.citeulike.org /user/akifumi/article/889740 (799 words)

	Catarina Rydin
		Her project examined the diversity, phylogeny and evolutionary history of seed plants, focusing on the Gnetales.
		With phylogenies as a framework Catarina studied correlations between cladogenetic events, morphological variation and biogeographical patterns.The origin and evolution of Gnetales is currently under intensive debate.
		Gnetales have been associated with angiosperms or with conifers, but their morphology is difficult to interpret and relationships and homology with other seed plants have never been fully understood.
	www.nrm.se /researchandcollections/palaeontology/palaeobotany/staff/catarinarydin.4.5fdc727f10d795b1c6e80007588.html (430 words)

	Hernandez Castillo: Anthophyte Hypothesis
		This molecular evidence implies a close relationship between conifers and Gnetales, where Gnetales could be nested within or even derived from conifers (called the "Gnepine" hypothesis).
		Reproductive structures of conifers are organized in cones, while gnetalean reproductive structures have been referred to as mega and microsporangiate cones, or even "flowers." Conifers have compound ovulate cones and simple pollen cones, while both gnetalean reproductive structures are compound.
		Questions such as the role of certain genes in molecular analyses, the validity of both molecular and morphological analyses, and the current status of morphological characters were addressed in the discussion.
	www.biology.ualberta.ca /courses.hp/biol606/OldLecs/Lecture2001.03.HC.html (645 words)

	Gnetophyta description (Site not responding. Last check: 2007-09-10)
		Crane, P. The fossil history of the Gnetales.
		Doyle, J. Seed plant phylogeny and the relationships of Gnetales.
		Endress, P. Structure and function of female and bisexual organ complexes in Gnetales.
	www.conifers.org /gnetales.htm (680 words)

	Encyklopedi :: Gnetales (Site not responding. Last check: 2007-09-10)
		Gnetales Plants, with a fossil record from the early Cretaceous, of particular interest because they show features of both conifers and angiosperms.
		It has been suggested that the Gnetales are the closest living relatives of angiosperms.
		There are 3 constituent genera, embracing trees, shrubs, and lianesrecord it is not surprising that the evolutionary relationships of Gnetales remain unclear.
	www.encyklopedi.net /Gnetales (136 words)

	Relationships among seed plants inferred from highly conserved genes: sorting conflicting phylogenetic signals among ...
		Relationships among major clades of seed plants are similar to those inferred from the parsimony analysis of the same data: angiosperms are sister to a clade that includes all gymnosperms and Gnetales and Pinaceae are sister taxa.
		Branches leading to terminal taxa of Gnetales and Moniliformopses, and of Pinaceae inferred from first and second positions, are also very long.
		Bowe L. Coat C. dePamphilis 2000 Phylogeny of seed plants based on all three genomic compartments: extant fymnosperms are monophyletic and Gnetales' closest relatives are conifers.
	www.amjbot.org /cgi/content/full/89/12/1991 (7905 words)

	[No title]
		Gnetales and flowering plants also similar in phenomenon of double fertilization.
		Ovules and female gametophytes of Gnetales are distinctive.
		In all three Gnetales, pollen tube grows downward through nucellus toward archegonium in Ephedra and egg in Gnetum and Welwitschia.
	www.d.umn.edu /biology/courses/bio3601/outlineMar21.htm (1592 words)

	MADS about Gnetales -- Frohlich 96 (16): 8811 -- Proceedings of the National Academy of Sciences
		By the 1930s, the Gnetales were in disfavor as close angiosperm relatives for a variety of reasons: e.g., the simple flowers
		Gnetales ovules are borne directly on a stem tip, whereas flowering-plant
		evidence that Gnetales are not sister to the angiosperms.
	www.pnas.org /cgi/content/full/96/16/8811 (2857 words)

	details
		For example, morphological studies consistently identify the Gnetales as the extant sister group to angiosperms (the so-called "anthophyte" hypothesis), whereas a number of molecular studies recover gymnosperm monophyly, and few agree with the morphology-based placement of Gnetales.
		All nuclear analyses strongly ally Gnetales with a monophyletic conifers, whereas all mitochondrial analyses and those chloroplast analyses that take into account saturation of third-codon position transitions actually place Gnetales within conifers, as the sister group to the Pinaceae.
		According to these findings, the Gnetales may be viewed as extremely divergent conifers, and the many morphological similarities between angiosperms and Gnetales (e.g., double fertilization and flower-like reproductive structures) arose independently.
	cmbi.bjmu.edu.cn /ChinaPaper/details.asp?PubMedID=10760277 (269 words)

	Phylogeny of New Zealand Plants (Site not responding. Last check: 2007-09-10)
		Morphological studies have traditionally placed the Gnetales as sister to the flowering plants based upon flower-like reproductive structure and double fertilization.
		However recent phylogenetic analyses of DNA sequence data suggest the Gymnosperms form a monophyetic group comprised of Ginkgo, cycads, conifers and Gnetales.
		The Gnetales emerge as sister to the conifers or in some cases are even nested within the conifers.
	plantphylogeny.landcareresearch.co.nz /webforms/ViewTree.aspx?ObjectID=b1200bb6-978f-421b-a4f6-248d3bb4602d (199 words)

	Ruhr-University Bochum, Lehrstuhl für Spezielle Botanik
		For decades, Gnetales appeared to be closely related to angiosperms forming the anthophyte clade.
		The interpretations of the male sporangiophores of Gnetales as pinnate with terminal synangia conflict with a close relationship of Gnetales and conifers.
		Therefore, it is obvious to interpret the male sporangiophores of Gnetales as simple organs with terminal synangia.
	www.ruhr-uni-bochum.de /boga/spezbot/MMTS2004A.html (265 words)

	Phylogeny of seed plants based on evidence from eight genes -- Soltis et al. 89 (10): 1670 -- American Journal of Botany
		Gnetales are sister to all other seed plants (Table 2).
		Doyle J. 1998 Molecules, morphology, fossils, and the relationships of angiosperms and Gnetales.
		Rydin C. Källersjö E. Friis 2002 Seed plant relationships and the systematic position of Gnetales based on nuclear and chloroplast DNA: conflicting data, rooting problems, and the monophyly of conifers.
	www.amjbot.org /cgi/content/full/89/10/1670 (6569 words)

	International Journal of Plant Sciences - Volume 157, Number 6, November 1996 - Supplement
		Wood, bark, and stem anatomy of Gnetales: a summary
		Double fertilization in Gnetales: implications for understan ding reproductive diversification among seed plants
		The morphology and evolution of male reproductive structures of Gnetales
	www.universityofchicagopress.com /IJPS/v157n6stoc.html (94 words)

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