Families of Vascular Plants - EEB337H

How do we study vascular plants in the field? This page still under construction

The "field" is anywhere outside the lab, the greenhouse or, in many cases, even a garden or experimental plot, where plants grow without human intervention, often as part of the natural vegetation of a place. Botanical fieldwork may take place almost anywhere, from the sidewalks and vacant lots or rooftops of the city, to the neighboring countryside, to the most remote parts of the world. Botanists and others visit these places in order to answer a variety of questions. In every case, answering questions will involve collecting data, often by means of some fairly simple and time-honored methods that are still of great value. These include...

Patterson Mountain Prairie, County, Oregon

Collecting herbarium vouchers and leaf tissue for DNA sequencing from a random sample of Crataegus suksdorfii at Patterson Mountain Prairie, Lane Co., Oregon. Photo by and © 2003 R. M. Love.


Collecting voucher specimens

Voucher specimens of vascular plants (and of Bryophytes) are entire plants, or portions of plants, that are sufficiently complete as to be representative of their species, and thus identifiable. Voucher specimens document that a particular species (known or unknown) occurred in a particular place at a particular time. For this reason almost every kind of scientific activity involving plants ultimately depends on the documentation provided by voucher specimens.

Voucher specimens of plants are also called herbarium specimens because they are stored in museums called herbaria. Herbaria and herbarium specimens are described in greater detail elsewhere, so for now it suffices to say that they are flattened, dried plants (or pieces of plants) that conform to a standard size and preserve many, if not all, of the features of the living plant. Complete herbarium specimens are mounted on sheets of heavy paper to protect them from damage, and include labels with details of the date and place of collection, as well as other information (e.g. other associated collections, identification, collector and collector's number, etc.). Herbarium specimen of Lythrum

Specimen of Lythrum alatum Pursh, TRT 197,611 (W. J. Cody 18446, collected 7 August 1969 with W. E. Kemp, Carleton Co., Ontario) . Annotations: (1) databased 1983 by staff of the Herbarium, Vascular Plant Section, Botany Division, Canadian Museum of Nature; (2) examined 1984 by C. J. Keddy in the course of preparing her 1987 treatment of Lythrum alatum Pursh for the Atlas of the Rare Vascular Plants of Ontario (Argus et al. 1982-1987). Lythrum alatum is rare in Canada, and this specimen represents the northernmost occurrence of the species in Ontario.

Voucher specimens are essential components of all scientific activity based on fieldwork. Voucher specimens document what species occur where, and when. Species in this context may be already known to science, or they may prove to have been discovered for the first time, based on comparison with other, already identified specimens in a herbarium. Herbarium specimens are the basis on which plant species are documented and recognized in classifications because they represent the plant as it is encountered in nature, interacting with its environment.

In an age of molecular systematics, when relationships between plants (same as, different from, sharing a nearer or a more distant common ancestor) can be inferred from DNA sequence data, it is vital to remember that DNA sequences by themselves, whether of coding regions or otherwise, are almost meaningless without information about the actual plant from which the DNA was obtained. Molecular phylogenies by themselves are expensive, time-consuming works of art rather than scientific documents if they cannot be related back to the organisms they represent. Voucher specimens, whether of plants, animals, or fungi, that are housed in museum collections (herbaria, etc.) provide the relationship between the abstract estimate of phylogeny and the organisms "out in the woods" that are the products of billions of years of evolution. Some of the reasons for this are indicated below.

Voucher specimens document morphology. Websites like the Angiosperm Phylogeny Website demonstrate the way in which the wealth of information about vascular plant phylogeny that has been derived over the last few decades from analyses of DNA sequence variation correlates surprisingly well with all sorts of chemical, ultrastructural, anatomical, and morphological features of plants. Knowledge of these features has been won over the past three thousand years or more as a result of human interactions with plants as sources of foods, drugs, fibers, fuels, as well as materials with which to build and make, to name just some of the uses to which plants are put by humans. Increasingly, over the history of human interactions with plants, this knowledge has been catalogued and systematized in relation to the visible, tangible form of plant species, as they grow, and as can be preserved in various ways for study, not the least as in the form of herbarium specimens. In other words, herbarium specimens document plant species as they are found in nature, and as they can be identified, described, and classified. X-ray images of Crataegus brachyacantha leaves

X-ray images of leaves of Crataegus brachyacantha Sarg. & Engelm. removed from a specimen collected in Texas by T. A. Dickinson. Upon closer examination the secondary and higher order veins can be see seen to form a unique pattern not found elsewhere in the genus. Images courtesy P. Ross and © 2007 Royal Ontario Museum.

Voucher specimens document variation. Naive persons sometimes suggest that a herbarium need only contain a single specimen of each species known to science in order to be complete. This suggestion ignores the the fact that plant species vary both in how and where they grow. At least some of the variation seen in how plants grow is due to the inheritable genetic variation on which natural (or human) selection can act. Variation in morphology can thus suggest hypotheses about evolution that can be tested with data from experiments: behavioral experiments involving the processes of growth and reproduction, or descriptive ones from which, say, data on DNA sequence variation can be obtained. Variation in where plant species can grow can suggest hypotheses about past or present environmental variation, or about the ways in which plants move from place to place.

Collecting tissue samples

We collect tissue samples, to give just three examples, (1) in order to document the ways in which plant species vary in chemical constituents that may have value as drugs, (2) in order to document critical features of growth and structure that may inform questions about the evolutionary significance variation, and (3) in order to provide material from which DNA can be extracted so as to infer phylogenetic relationships.

These tissue samples are meaningful only to the extent that they can be linked to voucher specimens collected from the same plant (or from the same population of the same species), ideally at the same time as the tissue samples were collected.

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Carrying out surveys

species distributions ->

recognition of ecoregions, e.g. papers by soper & fox re carolinian ontario Fig. 9 from Soper (1956) - Used with permission

 

Carrying out experiments

Stuart/Svenja pollinating image; Nadia experiments (TAD experiments)


| What are plant families? | How do we distinguish them? | How and why do we study them? | Selected vascular plant families of Ontario | Reading List | Course outline |

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Please send your comments to tim.dickinson@utoronto.ca; last updated 05-Sep-2008