a guide to the TREES OF MENLO COLLEGE By STUART A. OLSON MENLO COLLEGE menlo park, California Contents Introduction 1 Trees 2 Using a Key 3 Key to the Genera 5 Trees of Menlo College 13 Class Gymnospermae 14 Class Angiospermae 20 Glossary 37 Useful references 41 INTRODUCTION This book is written with the intention of teaching the botany student the methods and procedures involved in iden- tifying plants, and to familiarize the student with the species of trees found on the campus of Menlo School and College. Over 70 species of trees are represented on the Menlo campus. Of these, most are identified in this manual. Identi- fication of trees in this book is based primarily upon leaf structure and arrangement. Some species are difficult to iden- tify precisely without studying floral structure, or because their growth form may be atypical because of such factors as pruning, local environmental conditions, or because of the exis- tence of a great variety of horticultural forms. In these instances the trees are identified to the genus and are treated collectively (willows, cherry, plum, for example). Only fifteen species of the trees found on the Menlo cam- pus are native to the San Francisco Bay Area. The rest are introduced and represent types from many parts of the United States and the world. This gives the student an opportunity to become familiar with a wide variety of families of trees. TREES Plants are generally classified into two major groups: the Thallophyta, simple bodied plants with unicellular reproductive structures, and the Embryophyta, those plants which have more complex bodies, multicellular reproductive organs and produce an embryo in their life cycle. This latter group may be arbitrarily divided into non-vascular and vascular plants. The vascular plants are those which contain specialized structures, vessels, for conducting food and water throughout the plant body. The higher vascular plants may be divided into two more ar- bitrary groups: herbaceous, or soft-stemmed plants, and woody plants. VJoody plants are those which have vessels in which the cell walls have, in addition to cellulose, a chemical called lignin which makes them quite hard and rigid. Woody plants are found in the classes of seed plants known as Gymnospermae, which are all woody, and the Angiospermae or flowering plants which in- clude some woody and herbaceous plants. The woody plants are generally described as being either trees or shrubs. Although there is some overlap, a tree is usually considered to be a woody plant with a single main stem which is over fifteen feet tall at maturity. A shrub is usually a multiple stemmed woody plant which, at maturity, is less than fifteen feet tall. There is sometimes difficulty in determining whether a specimen is a small tree or a large shrub, and often the terms "tree-like" or "shrub-like" are used because of this. The plants described in this manual are, with few exceptions, limited to those which normally exist as trees by the above definition. USING A KEY There are several ways to learn the identity of a plant: 1) Ask someone who knows it: 2) Look at a collection of pic- tures; 3) Compare it to herbarium specimens if they are avail- able; 4) Use a key. Use of the keys in this book requires a rudimentary knowledge of some descriptive biological terms. These terms are included in the glossary at the end of the book. A key is a device used by the student of plant or animal taxonomy to identify groups or kinds of organisms. Many types of keys are used, and these are normally constructed so that organisms are arranged into groups with similar characteristics, and then broken down into smaller groups which have more speci- fic characteristics that distinguish the groups from one another. Eventually individual types are selected by traits which dis- tinguish them from other kinds. Most keys offer the user alternatives of choices. Keys are usually dichotomous, that is, the choices are paired. Each choice leads either to another pair of alternatives or to a final identification. The keys in this book are strictly dichotomous. Each pair of choices is numbered. Each choice is, essentially, a descrip- tion of a characteristic or group of characteristics with which the specimen to be identified should be compared. If the specimen fits the description for choice number one in a key, the student should then go on to the next description which immediately follows the first. If the specimen does not fit, then the student should go on to the second choice number one. It is always wise to read both members of a pair of descrip- tions and select the most accurate. "Keying" is more an art than a science. As one progresses through the keys in this manual, he is led from one set of alternatives to another, and ultimately to the genus of the plant in question, with a page reference. In turning to that page he will find a description of the species of trees in that genus that are found on the campus of Menlo Col- lege and the identification is complete. KEY TO THE GENERA 1. Leaves parallel veined and arising from the summit of the main trunk or its branches (MONOCOTS) Page 7 1. Leaves net-veined or not distinctly parallel veined, arising from branches or branchlets. 2. Leaves compound Page 8 2. Leaves simple 3. Leaves less than 3/8 inch wide, ovate, linear, needle-like, awl-shaped or scale-like 4. Leaves not scale-like Page 6 4. Leaves scale-like, surrounding branchlets Page 7 3. Leaves more than 3/8 inch wide 5. Leaves opposite Page 8 5. Leaves alternate Page 9 LEAVES NOT SCALE-LIKE 1. Leaves needle-like, in clusters on branches 2. Leaves usually more than 2 inches long, in bundles of 2 to five Pinus Page 17 2. Leaves usually less than 2 inches long, in clusters of more than 5 needles (some single needles on young shoots Cedrus Page 16 1. Leaves all single (never in clusters) on branches 3. Leaves linear, 1/4 to 3/8 inch wide, over 1-1/2 inches long, fruit a legume Acacia Page 32 3. Leaves less than 1/4 inch wide 4. Leaves awl-shaped 5. Free part of leaf less than 1/4 inch long, bases adherent to stem (decurrent) Sequoiadendron Page 15 5. Leaves spreading from stem, spirally arranged and overlapping giving smaller branchlets a rope-like appearance Araucaria Page 14 4. Leaves linear or narrowly lanceolate 6. Leaves, when removed, leaving round scars on branches; cones with 3 pointed bracts pro- truding from cone scales Pseudotsuga Page 17 6. Leaves not leaving round scars when removed 7. Leaves stiff, sharp and 4-angled, leaving short distinct pegs on branches when falling Picea Page 16 7. Leaves more flexible, often pointed but not stiff and prickly to the touch 8. Leaves attached to branches by decurrent bases 9. Leaves with short petioles, continuous with bases, falling singly .... Taxus Page 14 9. Leaves sessile, persistent, falling with branchlets Sequoia Page 15 8. Leaves with distinct petioles attached by stalk-like processes to sten Pseudotsuga Page 17 LEAVES SCALE-LIKE, SURROUNDING BRANCHLETS 1. Branchlets forming decidedly flat sprays 2. Leaves apparently 4 at a node, internodes longer than broad Libocedrus Page 18 2. Leaves 2 at a node, internodes about as long as broad 3. Cones oblong with overlapping scales; branchlets over 1/12 inch thick Thuja Page 18 3. Cones globular, peltate; branchlets less than 1/12 inch thick Cupressus Page 18 1. Branchlets not forming flat sprays 4. Leaves more awl-shaped than scale-like, spirally arranged, 1/4 to 1/2 inch long Sequoiadendron Page 15 4. Leaves definitely scale-like, 2 at a node...Cupressus Page 18 MONOCOT TREES 1. Leaves not divided 2. Leaves 1-1/2 to 3 feet long, 1 to 2-1/2 inches wide, drooping against trunk and turning brown with age.. Cordyline Page 20 2. Leaves 1 to 2 feet long, 1 to 1-3/4 inches wide, fairly rigid, sword-shaped, leather Dracaena Page 20 1. Leaves divided (Palms) 3. Leaves fan-shaped (palmate) 4. Tall smooth stemmed trees, old leaves hanging against stems Washingtonia Pj-ge 21 4. Shorter plants, stems hairy and covered with old leaf bases 5. With a single main trunk; petioles armed with long sharp spines Chamaerops Page 20 X 5. With several stems branching very near baser,fI petioles^ y often with small teeth but not spines ... \fr Trachyci^rpus Page 21 3. Leaves pinnate (Feather palms) 6. Trunk covered with old leaf bases Phoenix Page 21 6. Trunk smooth Jubaea Page 21 LEAVES COMPOUND 1. Leaves twice-pinnately compound, less than 4 inches wide, prominent glands on upper side of rachis Acacia Page-32 1. Leaves once pinnately compound 2. Larger leaflets usually over 2 inches long 3. Leaflets entire 4. Leaflets alternate, petiolulate.... Cladrastis Page 33 4. Leaflets sessile, opposite Juglans Page 23 3. Leaflets toothed or lobed 5. Leaflets less than 1/2 inch wide; fruit a drupe, in clusters Schinus Page 34 5. Leaflets over 1/2 inch wide; fruit a nut ... Juglans Page 23 2. Larger leaflets usually less than 2 inches long 6. Leaflets entire, over 1/2 inch wide; plant usually thorny Robinia Page 33 6. Leaflets toothed, less than 1/2 inch wide... Schinus Page 34 LEAVES OPPOSITE 1. Leaves palmately lobed and veined Acer Page 34 1. Leaves not lobed, entire 2. Leaves less than 3 times longer than broad, lateral veins curving upward toward apex Cornus Page 35 2.