Trees and shrubs in winter

 

How can one identify deciduous oaks, maples or other trees in winter? Botanists work with all kinds of plants that might be at various stages of growth and development or in different states throughout the year. And you can find all of these stages represented in our collections at the Herbarium, from seeds to seedlings, in growth and dormant. Many plants may be readily identified when they are in flower and/or fruit, or cone, as in conifers, or with spore cases, as in mosses and ferns. Many of these plants are photogenic, especially in Spring and during the bright summer days. After autumn however, they lose their colorful and identifying winterscene-widemarks, but this does not mean that they lose their identity. They can be distinguished from each other, particularly if they are trees and shrubs and not members of large species groups. This may be difficult to the untrained eye, but botanists pay attention to them in their denuded states as well, or when they are just beginning to emerge from the ground, and just before producing flowers, cones or spore cases. Some individuals, particularly those working with wood and in forestry, need to know about dormant plants as they are likely to meet them in their field excursions in autumn and winter.

How do these plants look in winter and how are they identified? Here we present some notes and images of plant parts, particularly when these are in their least photogenic states, and show how botanists recognize them. One of the early works on this topic is a book by William M. Harlow, who produced an illustrated key to buds, twigs and fruits — in winter condition in the first two cases.

Leafless plant structures or parts. Some of the structures or parts that can be utilized in identifying plants in winter condition are buds and bud scale scars, leaf and stipular scars, fruit scars, the surface structure of twigs and the sectional outline, composition and shape of the inner part of the twig called pith, the locations of sharp outgrowths on the twigs (spines, thorns or prickles) and presence or absence of short shoots.

Buds that remain on the twigs in winter are embryonic structures; most are covered with scales, which are modified or thickened leaves. Buds are usually situated at the apex of the stem or branch, or laterally on a twig. There are also those that appear terminal but are not since growth in spring continues laterally and the buds open up and grow to be lateral branches or terminate into flowers. These are often called false terminal buds. Terminal buds are usually larger than the laterals.

falseterminallateral

Lateral buds appear in three arrangements: those occurring in 3’s or more are called whorled buds; those that occur singly along the twigs are called alternate buds, and those occurring in pairs at approximately 180o from each other are called opposite buds. In all of these, except the terminal bud or buds, leaf scars are situated beneath each bud.arrangement

Bud scale scars are marks left from the previous season’s growth, resulting from the terminal bud. They appear as single lines at the end of last year’s growth. Leaf and stipular scars. When a leaf falls off in autumn, a narrow area, a scar, is left on the twig indicating budscarwhere the leaf was attached. These scars are of different types or shapes. Some plants have tiny, leaf-like structures on each side of a leaf. When these fall off in autumn, they also form scars on each side of the leaf scar. In some species, these form a circle.

Twig surfaces, sectional outline and pith. Many plant twigs have pale white wart-like growths on their surfaces. These are called lenticels and are areas of loose cells that the plant utilizes to draw in or send out gases such as carbon dioxide and oxygen. Their presence or absence and their particular structure are applied in identifying twigs. Dissecting the twig cross-wise and along the long-axis displays the inner core and the cellular composition of the twig. Some may be filled with tissue, called pith. Others may be devoid of this. The pith may be solid or compartmentalized.

lenticelssolidchambered

Pointed outgrowths on twigs. Spines and thorns arise from a region on the twig called the node while prickles may arise anywhere between two nodes. If a bud is found between the twig and the pointed outgrowth, then that pointed outgrowth is considered a spine as it represents a modified leaf. If the  outgrowth is in the position of a bud and there is a scar beneath it, then it is a modified stem, called a thorn with the scar representing the position of the fallen leaf. Prickles are hardened or modified surface cells arising anywhere on the twig.

spinethornprickle

Short or spur shoots. These are branches that have been growing very slowly along any of the main branches. In terms of composition, they are similar to any of the twigs but have very condensed growth of leaves. spurWhen the leaves fall off, they leave behind dense linear scars. They are often called spur shoots and are common in ginkgo (as shown here), cherry, apple and birch trees.

By examining the combinations of these features, as well as features such as color of bark and shape of buds, we are able to identify woody plants when they are dormant.  This is true whether the plants are still growing outdoors or have been preserved as specimens in the collection.

 

About the authors:  Mesfin Tadesse is Curator of Seed Plants in the OSU Herbarium and Robert Klips, who provided the photos, is Associate Professor in EEOB at the Marion Campus.

 

Plants that we have been working on for the past few years

 

For this week’s photo gallery I decided to share images of some of the plants that my students and I have been working on for the past few years.  Some of these projects are now finished and some of them are ongoing.  Luckily, we often work on photogenic groups!

 

About the AuthorDr. John Freudenstein is a Professor in the Department of Evolution, Ecology and Organismal Biology and Director of the OSU Herbarium.  All photos are by the author.

Plants in Flatland; or the ups and downs of turning organisms into paper

 

In 1884 Edwin Abbott published a satirical novel about Victorian life entitled “Flatland: A Romance of Many Dimensions” in which he described a fictional two-dimensional world and one character who realizes that a third dimension exists – but is unable to persuade others. In many ways the Herbarium collections belong to such a world – after all, unlike all of the other collections in our Museum, the Herbarium consists largely of plants that have been robbed of one of their dimensions!

Why is this? Nobody would think of flattening a whole insect or a squirrel or a fish as a method of preservation. What is it that all of them have that plants do not have? A skeleton. Whether on the inside (endo-) like we have, or on the outside (exo-) as arthropods have, many animals have a skeleton that allows them to keep their shape even when dead. Remember that vase of roses that dried out while you were away on vacation, only to present itself as a withered and curled jumble of brittle parts when you returned? That’s what would happen if we allowed plants to dry as three dimensional objects.

A plant press used for preparing specimens.

A plant press used for preparing specimens.

This situation leaves us with two choices: either we preserve plants in a liquid such as alcohol or we press and dry them. Liquid preservation would keep the third dimension, but liquid (“spirit” as they are often called) collections are care-intensive in that the fluids must be constantly checked to be sure that they do not evaporate. Maintaining jars with fluid also takes a significant amount of space. Lastly, even in a preservative fluid plant tissues eventually begin to disintegrate, so it is not the best choice for the long term. The standard method of pressing and drying plant specimens was established long ago and it is a good compromise.

Yes, even cacti need to be pressed!

Yes, even cacti need to be pressed!

Pressing is an essential part of the drying process because it keeps the tissues from experiencing the distortion that differential loss of water would otherwise cause (remember those withered roses?). The majority of a plant’s body is made up of cellulose – it’s the fibrous part that you cannot digest – and this provides structure to the plant while alive and also when it is dried. The lack of such a handy molecule is the reason that we cannot just dry those animals that do not have some sort of skeleton – invertebrates such as sea anemones, worms, and many others. They are largely protein and fats in composition and those molecules just do not provide structure. They dry to a useless blob of crispy tissue. Think of those dried squid pieces from your local Asian foods grocer – can you imagine trying to study those?

So we press and we dry. The faster we dry, the better, in terms of preserving colors and also molecules that we might be interested in, such as DNA. Today, herbarium collections are a valuable source of DNA for comparative studies, so we do think about trying to preserve specimens for that use. Even when dried carefully, a plant specimen’s colors will eventually fade and of course features such as floral scent do not preserve, which is why it is important to note any aspects of the plant that might not last on the label that accompanies the specimen.

And it works – we are essentially turning the plant into paper and as long as the specimen is kept dry and away from insects that might eat it, it should keep indefinitely.

A specimen from 1560 from the Natural History Museum in Kassel.

A specimen from 1560 from the Natural History Museum in Kassel.

The earliest plant specimens in existence are from the mid-1500’s and they are doing just fine. In fact, the oldest herbarium collection is at the Natural History Museum in Kassel, Germany, where the oldest specimens are bound in books, as they were typically in the early days. Here at OSU the oldest plant specimens in our collection are from 1839-40, collected by William Starling Sullivant from the area around Columbus.  Today there are tens of millions of herbarium specimens worldwide, all preserved in this way, many now being imaged and databased for easy remote access.

But we still miss that third dimension. Students sometimes express frustration in getting used to looking at pressed plants. I have been doing it for so long that it is second nature. But I can remember at first trying to relate that flattened object to something living – it was challenge. And it still can be. It turns out that some species differ in rather subtle ways that involve orientation of floral parts that is completely obscured in pressing. Luckily, some flowers can be rehydrated by removing from the specimen and just bringing to a boil in a little water.

Our native Snow Trillium (T. nivale), only 3 inches tall.

Our native Snow Trillium (T. nivale), only 3 inches tall.

Some flowers essentially spring right back into three dimensions when this is done, which is great. Unfortunately, not all do. Some flowers are very thin-textured and although they dry just fine, trying to rehydrate them results in a shapeless mass of mush. Not surprisingly, those groups are often the ones that have not been worked on scientifically because so much of the study needs to be done in the field, with specimens being less useful. An example of flowers that do not rehydrate well is our North American genus Trillium because the petals have a very thin texture.

In the end, any method of preservation of an organism will result in some loss of information. However, we can learn so much from what we do preserve and our collections can so broadly extend sampling beyond what any one person could ever see in the field. So we live with our limitations and, unlike the Flatlanders, we believe that there are many more dimensions waiting for us out there in the field.

 

About the AuthorDr. John Freudenstein is a Professor in the Department of Evolution, Ecology and Organismal Biology and Director of the OSU Herbarium.  All photos are by the author.