Peter Raven

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Papers by Peter Raven

The Systematics and Anatomy of Gongylocarpus (Onagraceae)

American Journal of Botany, 1966

The unique fruiting structures of the closely related, principally Mexican, monotypic genera Gong... more The unique fruiting structures of the closely related, principally Mexican, monotypic genera Gongylocarpws and Burragea (Onagraceae) compelled a detailed anatomical and cytological investigation of these plants which led to the conclusion that they should be included in a single genus, Gongylocarpus. Gongylocarpus fruticulosus (Burragea), endemic to two adjacent islands off the west coast of Baja California, is divided into two subspecies, subsp. fruticulosus and subsp. glaber. The vegetative and floral anatomy, including wood anatomy, of both species is described. The fruits of these two species grow into the stem by meristematic activity during the course of ontogeny, the ovaries in the mature flower being superficial and sessile in the leaf axil. There is no pedicel associated with the flower, but only a branch gap. Meristematic tissue at the base of the locules divides rapidly at a relatively late ontogenetic stage, the ovaries growing downward into the stem and crushing the pith. The mature, heavily sclerenchymatous fruits are located wholly within the stem, and in G. fruticulosu.s they are aggregated into long chains. Both species have a gametic chromosome number of n = 11, a characteristic otherwise unknown in the tribe Onagreae but shared with other generalized groups in the family. Taken together with other features, this suggests a primitive position within the tribe for Gongylocarpus.

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Reinterpretation of the Type of Godetia bottae Spach (Onagraceae)

Annals of the Missouri Botanical Garden, 1977

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IV. Pope Francis’ Encyclical Letter Laudato Si’, Global Environmental Risks, and the Future of Humanity

The Quarterly Review of Biology, 2016

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Embryology of Onagraceae (Myrtales): characteristics, variation and relationships. Telopea 8:667-688

Telopea

Here we report features of the embryology of 14 genera of Onagraceae, as a companion study to our... more Here we report features of the embryology of 14 genera of Onagraceae, as a companion study to our earlier report on Ludwigia alone. We found that the 4-nucleate Oenothera type embryo sac that sharply distinguishes Onagraceae from all other Myrtales is common to all genera. Shared features of the nucellus and seed coat structure, however, indicate that Onagraceae more closely resemble Lythraceae than other Myrtalean families. Differences between onagraceous genera are found in 1) the mode of anther wall formation (the Basic or the Monocotyledonous type), 2) the number of cells in the ovule archesporium (one-celled or multi-celled), 3) the nature of early development of the inner integument (retarded or not retarded), and 4) the thickness of the parietal tissue in the nucellus (thin or thick). Based on comparisons in these and other embryological characteristics, we have concluded that: 1) Ludwigia (Jussiaeeae) differs sharply from the rest of the family in having a one-celled archesporium in its nucellus; 2) Hauya (Hauyeae) and eight of the genera of Onagreae (except Gayophytum) closely resemble one another but differ from the other genera of the family in their markedly thick parietal tissue in the nucellus; 3) Gayophytum, unlike other Onagreae, resembles Epilobium (now including Boisduvalia) in having retarded early development of its inner integument and in having thin parietal tissue; 4) Clarkia heterandra (formerly segregated as the monotypic genus Heterogaura) differs from other species of Clarkia and from other Onagreae (except Gayophytum) in its nucellar histology.

format_quoteNotable differences in nucellar tissue thickness among Onagraceae genera reveal diversity in developmental strategies.format_quote

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Checklist of the grasses of India

PhytoKeys

A checklist of the grasses of India is presented, as compiled from survey of all available litera... more A checklist of the grasses of India is presented, as compiled from survey of all available literature. Of the twelve subfamilies of grasses, ten are represented in India. Most subfamilies have been examined by taxonomic experts for up-to-date nomenclature. The list includes 1506 species plus infraspecific taxa and presents information on types, synonyms, distribution within India, and habit. Twelve new combinations are made, viz. Arctopoa tibetica (Munro ex Stapf) Prob. var. aristulata (Stapf) E.A. Kellogg, comb. nov.; Chimonocalamus nagalandianus (H.B. Naithani) L.G. Clark, comb. nov.; Chionachne digitata (L.f.) E.A. Kellogg, comb. nov.; Chionachne wallichiana (Nees) E.A. Kellogg, comb. nov.; Dinebra polystachyos (R. Br.) E.A. Kellogg, comb. nov.; Moorochloa eruciformis (Sm.) Veldkamp var. divaricata (Basappa & Muniv.) E.A. Kellogg, comb. nov.; Phyllostachys nigra (Lodd. ex Lindl.) Munro var. puberula (Miq.) Kailash, comb. & stat. nov.; Tzveleviochloa schmidii (Hook. f.) E.A. Kello...

format_quoteThe checklist comprises 1506 grass species in India, with taxonomic updates, including twelve new combinations made during the research.format_quote

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Plants make our existence possible

PLANTS, PEOPLE, PLANET

Maintaining biodiversity will define our long-term success

Plant Diversity

Phylogenetic patterns suggest frequent multiple origins of secondary metabolites across the seed plant “tree of life”

National Science Review

To evaluate phylogenetic patterns of the distribution and evolution of plant secondary metabolite... more To evaluate phylogenetic patterns of the distribution and evolution of plant secondary metabolites (PSMs), we selected 8 classes of PSMs and mapped them onto an updated phylogenetic tree including 437 families of seed plants. Significant phylogenetic signal was detected in 17 of the 18 tested seed plant clades for at least one of the 8 PSM classes using the D statistic. Phylogenetic signal, nevertheless, indicated weak clustering of PSMs compared to a random distribution across all seed plants. The observed signal suggests strong diversifying selection during seed plant evolution and/or relatively weak evolutionary constraints on the evolution of PSMs. In the survey of the current phylogenetic distributions of PSM, we found that multiple origins of PSM biosynthesis due to external selective forces for diverse genetic pathways may have played important roles. In contrast, a single origin of PSM seems rather uncommon. The distribution patterns for PSMs observed in this study may also ...

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Saving plants, saving ourselves

Plants, People, Planet

Who is better prepared than plant scientists to care for our common garden in the face of environ... more Who is better prepared than plant scientists to care for our common garden in the face of environmental threats that must be overcome? Regardless of how important our short-term goals may seem, we are citizens of a world in which a large proportion of other living forms are moving rapidly toward extinction. Collectively, human beings have created a world in which only our very best efforts will ensure peace, prosperity, and sustainability for ourselves and those who will follow us. The possibility of building a durable future may still be within our grasp, but only if we undertake a level of collective effort and cooperation much greater than anything we have attempted thus far. In July 2017, a group of plant scientists gathered in Shenzhen for an especially productive meeting, the first International Botanical Congress held in China. Here, I shall review the Shenzhen Declaration, a series of suggestions for how plant scientists might contribute to the overall human effort, endorsed by the Delegates at the conclusion of the Congress (Shenzhen Declaration Drafting Committee, 2017). These

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Europe's renewable energy directive poised to harm global forests

Nature communications, Jan 12, 2018

This comment raises concerns regarding the way in which a new European directive, aimed at reachi... more This comment raises concerns regarding the way in which a new European directive, aimed at reaching higher renewable energy targets, treats wood harvested directly for bioenergy use as a carbon-free fuel. The result could consume quantities of wood equal to all Europe's wood harvests, greatly increase carbon in the air for decades, and set a dangerous global example.

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When the cure kills-CBD limits biodiversity research

Science (New York, N.Y.), Jan 29, 2018

Taxonomy of many species of Rhododendron from the Himalaya (four are seen flowering) is uncertain.

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Genome skimming provides new insight into the relationships in Ludwigia section Macrocarpon, a polyploid complex

American journal of botany, Jan 23, 2018

Interpreting relationships within groups containing polyploids, which are frequent in angiosperms... more Interpreting relationships within groups containing polyploids, which are frequent in angiosperms, can be greatly assisted by genomic techniques. In this study, we used a genome-skimming approach to investigate the evolutionary relationships and origins of polyploids in the monophyletic group, Ludwigia section Macrocarpon (Onagraceae), which includes diploid, tetraploid, and hexaploid taxa. We sampled all known taxa and ploidy levels in the section and conducted shotgun sequencing. We assembled plastomes, mitochondrial sequences, and completed nuclear ribosomal regions, reconstructed phylogenies, and conducted comparative genomic analyses for plastomes to gain insights into the relationships among studied taxa. Within the section, results showed that the South American diploid taxa L. bonariensis and L. lagunae were closely related. We reported the first chromosome count (2n = 4× = 32) for L. neograndiflora, which is closely related to the two South American diploid taxa, although i...

An integrated assessment of the vascular plant species of the Americas

Science (New York, N.Y.), Dec 22, 2017

The cataloging of the vascular plants of the Americas has a centuries-long history, but it is onl... more The cataloging of the vascular plants of the Americas has a centuries-long history, but it is only in recent decades that an overview of the entire flora has become possible. We present an integrated assessment of all known native species of vascular plants in the Americas. Twelve regional and national checklists, prepared over the past 25 years and including two large ongoing flora projects, were merged into a single list. Our publicly searchable checklist includes 124,993 species, 6227 genera, and 355 families, which correspond to 33% of the 383,671 vascular plant species known worldwide. In the past 25 years, the rate at which new species descriptions are added has averaged 744 annually for the Americas, and we can expect the total to reach about 150,000.

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Extinction by numbers

Nature

H I is expected to become largely molecular (H 2) before forming stars. Star formation is also an... more H I is expected to become largely molecular (H 2) before forming stars. Star formation is also an inefficient process, so lots of molecular gas should be left over. By far the most abundant chemical in a molecular cloud is H 2 , but it does not radiate detectable energy at typical cloud temperatures of 20-50 K. Like other astronomers, Braine et al. have to infer the amount of H 2 by observing radiation from accompanying trace molecules, principally carbon monoxide (CO). Crucial to this procedure is the assumed ratio of H 2 to CO in the cloud. This

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Observations on the Chromosomes and Relationships of Hauya and Xylonagra

Aliso

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The Typification of Zauschneria Californica

Aliso

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Appreciation of a Great Man: Wu Zhengyi (1916–2013)

Plant Diversity

Comparative Reproductive Morphology of "Orias" and Lagerstroemia (Lythraceae)1)1)Dedicated to Prof. Dr. H. Meusel on the occasion of his 80th birthday

Flora

Structure and Macromolecular Composition of the Seed Coat of the Musaceae

Annals of Botany

Mature seed coats of representatives of all three genera of Musaceae were analysed for macromolec... more Mature seed coats of representatives of all three genera of Musaceae were analysed for macromolecular composition with various mass spectrometric techniques and compared with scanning electron microscopy and light microscopy in combination with histochemical techniques. Mass spectrometric techniques are more sensitive and more specific in identifying macromolecular compounds than histochemical methods. The macromolecular ' fingerprint ' of the seed coats of Musaceae showed unique components of aromatic phenols. The seed coat structure of all three genera is homogeneous within the Musaceae. It is characteristic at the family level and most complex within the Zingiberales. Very remarkable are the separation of the outer cell walls from the exotestal layer, exposing a secondary surface with silica crystals, and the relatively thick mesotesta which protects the seed, e.g. against the biting forces and passage through the digestive tracts of dispersing agents. Germination takes place with an operculum and is facilitated by a predetermined rupture layer in the micropylar collar. The musaceaous seed presents a good example of the solution of conflicting demands of protection and germination.

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The Fate of the World's Plants

Trends in ecology & evolution, May 3, 2017

A recent report assessing the world's plant species finds continuing progress in completing t... more A recent report assessing the world's plant species finds continuing progress in completing the taxonomic catalog. However, many undescribed species remain. The report concludes that, presently, 21% of known species risk extinction. We show this statement applies to the short-term and ignores the as-yet undescribed species, which are also likely at risk of extinction. Human actions will extirpate many more by the end of this century.

Peter Raven

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