Archaeological Parenchyma

Jon G Hather

• Publisher: Routledge
• Year: 2016
• eBook ISBN: 9781315434476
• Topic: Social Sciences
• Subtopic: Archaeology
• Index: Social Sciences

The parenchymous remains of roots and tubers are increasingly becoming recognized as an important category of plant remain alongside seeds, fruits and wood charcoal. Identification is however frequently viewed as problematical and such important indicators of past diet are often left unidentified. This book describes the full range of anatomical and morphological characters used in the identification of the parenchymous remains of roots and tubers. Each of the characters is illustrated by photographs of modern and archaeological plant tissues and by line drawings. Further sections of the book also deal with the examination of archaeological tissues and the preparation of modern plant tissue reference collections.

1

CHAPTER ONE

Introduction

Parenchyma as a plant remain

The examination, identification and interpretation of the remains of plants from archaeological and palaeoenvironmental contexts is commonly separated into the individual analyses of different plant tissues and organs; wood, seeds and fruits, leaves and bud scales, pollen and so on. This is largely because of the way in which plants are used by people and also the way in which they become preserved in archaeological and off-site contexts. This is generally different from the more taxonomic way in which the archaeological remains of animals are analysed – large mammals, small mammals and various classes of invertebrate. Technical improvements in methodology and an increasing interest in a more holistic approach to archaeobotanical investigation has led to a significant increase in such classes of plant remains that are routinely identified. This breadth of analysis adds significantly to the accuracy of interpretation though it may often require collaboration between specialist archaeobotanical analysts.

Vegetative storage parenchyma, a specific type of plant tissue, is a major constituent of one class of plant remain (see Figure 1). Parenchyma is the botanical term for a relatively undifferentiated tissue, composed of many similar thin-walled cells. These are often polyhedral and broadly isodiametric in shape which together form a ground tissue that surrounds other tissues. Parenchyma occurs in many different plant organs in varying amounts. Large fleshy organs such as fruits and many roots and stems are composed largely of parenchyma. Wood, and the tissues that make up organs such as leaves and flowers also contain parenchyma but this may be more sparse and may often be specialised. Vegetative parenchyma is that which is found in plant parts that are not directly part of the non-vegetative propagule, i.e. that which has been produced by fertilisation. Seeds and true fruits, therefore, do not contain vegetative parenchyma although flower parts do. The vegetative storage parenchyma in swollen roots and stems stores starch and other carbohydrates and sugars which have been gathered and cultivated as food by people throughout the past (see Figures 2 and 3). Its occurrence on archaeological sites is of relatively recent report (e.g. Martins 1976) though it has already proved to be important as both as evidence for past subsistence and as an indicator of the origin and dispersal of particular crop plants.

Vegetative parenchymous storage organs vary greatly in morphology for both functional and phylogenic reasons; a systematic classification of these organ types is presented in Chapter 2. However, a convenient, though often misleading, handle is often used as a generic term for plant organs containing vegetative storage parenchyma – ‘roots and tubers’. The term is useful since it immediately focuses attention upon the type of organs containing vegetative storage parenchyma. However, it is also a morphological over-simplification and in some contexts requires clarification. Replacing the term would not attract 2a great deal of sympathy, particularly from those who see botanical terminology as a hindrance to understanding science rather than as an aid; so it is used here but with caution. I hope that Chapter 3 will demonstrate the term’s shortcomings in presenting accurate archaeobotanical description.

Figure 1 Charred remains of Brassico campestris ssp. ropo tuber (turnip) (Cruciferae) from Sparta, Greece. Scale = 1.40 cm (Hather et al. 1992). The remains of turnip from Byzantine levels (context EW9) of Sparta were identified by characters of both the anatomy and the morphology. The tuber is a combination of swollen stem and root tissue (see Figure 43) and is made up largely of parenchyma cells.

Figure 2 The rhizome of Typha ongustifolio (Typhaceae) being split open to show the ‘spongy’ cortex and starchy stele. Typha rhizomes have been modelled as a likely starchy resource for hunter-gatherers in both North America and Europe and the Near East (e.g. Turner 1981). Remains of Typha have been recovered from Early Chalcolithic levels at Can Hassan 1, Konya Plain, Turkey (sample 814B) (see Figures 145 and 146).

Figure 3 The tubers of Dioscoreo pentophyllo (Dioscoreaceae) being dug up in the Highlands of Papua New Guinea. Tubers of the Dioscoreaceae and corms of the Araceae form the principal staples of horticultural systems of the Indo-Pacific tropics (Hather 1996).

How to use this book

The aim of this book is to provide a detailed description of the morphological and anatomical characters used in the identification of charred vegetative parenchymous organs. Since it draws examples from a range of temperate and tropical regions from around the world, the identification of root and tuber remains from one specific region is beyond its remit. Similarly this book does not pretend to give an exhaustive review of root and tuber identification on a worldwide basis. What is presented here is, perhaps, somewhere between the two – it gives the basis for identification of root and tuber remains from an anatomical and morphological perspective which could just as easily be applied to the North American flora as to 3that of the Indian sub-continent. This book is aimed at those who are seeking to identify root and tuber remains, preserved by charring, in the archaeological record. It provides, through Chapters 2 to 7, detailed discussion of the morphological and anatomical characters by which root and tuber remains are identified. Its focus is neither regional nor floristic. Rather it aims to present a more general view of root and tuber identification. With this in mind the final chapter deals with practical methods of making a reference collection and technical aspects of preparing material for examination for both optical and scanning electron microscopy.

This book does not deal with waterlogged remains of vegetative parenchymous remains. Although the anatomical descriptions of the modern tissues are, of course, relevant, the identification of waterlogged remains, the survival of characters during the charring process and their identification, a major aspect of the work presented here, is not. The survival of diagnostic characters in waterlogged environments has yet to be explored in detail.

The identification of the remains of vegetative storage parenchyma is achieved by the recognition and comparison of diagnostic characters of a plant’s morphology and anatomy. The use of such characters in traditional plant systematics has long been recognised as being of enormous value, although the nature of the characters employed to identify archaeological remains differ from such use in a number of significant ways.

(i) Plant systematicists have access to characters of the whole plant from different stages of its life cycle, whereas archaeological remains usually present a sub-sample of these characters in the form of fragments of the whole plant from a single stage in its life.

(ii) Plant systematicists will usually use characters of the inflorescences, seeds and fruiting structures, stems and leaves of a plant. This is for two reasons: first flowers, fruits and leaves etc. vary greatly in stable morphological characters and secondly, they are easier to collect and preserve. For the archaeobotanical identification of such plant parts this is useful but for vegetative parenchymous storage organs, little diagnostic data has been published.

(iii) The way in which plant remains are preserved in archaeological contexts is such that some characters of traditional use will be absent or made difficult to observe, for example the archaeological remains of leaves may rarely bear trichomes that are often vital in systematic anatomy, though otherwise the leaf may be perfectly preserved.

The morphology of a plant is its outward appearance at the level of its constituent organs. It may take a purely descriptive approach or address issues of development, ecological and environmental adaptation, evolution, function and so on. The anatomy of a plant deals with the constituent cells and similarly may deal with issues of development and function. Both morphology and anatomy are of diagnostic value in the identification of roots and tubers. It is worth noting here also that a plant’s anatomy is reflected in its morphology and that morphology is reflected in anatomy.

This book makes frequent use of photographic illustrations, light micrographs and scanning electron micrographs as well as line drawings and flow diagrams: both plant anatomy and plant morphology are very visual disciplines. The illustrations and their captions are not there simply to support the text – they are as important an aspect of the book as the text. Not only would this book be much less informative with fewer illustrations, it would be impossibly tedious.

Cells and tissues – an introduction to vegetative soft tissue anatomy

The plant body is made up of tissues comprising cells of varying form and function (see Figures 4, 5 and 6). The identification of these cell and tissue types, their organisation, relative abundance and variation in form and the diversity of these characters in different taxa underlies the basis of systematic plant anatomy. The way in which the whole plant body and individual organs develop throughout its life cycle, from the initial stages of growth at germination through to senescence, is the basis of developmental plant anatomy and is also of great significance in systematic anatomy. Throughout the whole plant body there are relatively few different cell types but the variation in the nature of the tissues they form and the organisation of these tissues within different plant organs is vast. There are three main tissue types in vegetative storage organs: parenchyma, sclerenchyma and the vascular tissues. Each have a different structure and function:

Table 1 Tissue types in vegetative storage organs.

Tissue		Relative wall thickness	Function
Parenchyma		thin walled	packing / storage /turgidity
Sclerenchyma		thin walled	support/defence
Vascular tissues	Xylem	thick walled	transport
	Phloem	thin walled	transport

The vascular tissues are more complex than the tissues of the parenchyma and sclerenchyma. They comprise two types of conducting tissues: the xylem which has the function of the translocation of water and solutes, and the phloem which has the function of the translocation of sugars and nutrients. The xylem comprises vessel elements, tracheids and fibretracheids. The phloem comprises sieve tubes and companion cells. Both tissues may also contain varying amounts of sclerenchyma and par...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Contents
• Table of illustrations
• Acknowledgements
• 1 Introduction
• 2 Gross morphology
• 3 Surface morphology
• 4 Parenchyma
• 5 The vascular tissues of the stem
• 6 Root tissues
• 7 Sclerenchyma
• 8 Practical methods
• Glossary
• References
• Index