6 
PLANTS OF YELLOWSTONE NATIONAL PARK 
PLANT STRUCTURES 
Although we have attempted to make this book as nontechnical 
as possible, it is necessary to recognize the fact that anyone who 
wishes to identify wild flowers efficiently must first know something 
of the language of the botanist; the language that the botanist uses 
in describing plants. The glossary which begins on page 140 will 
be found very helpful in becoming acquainted with many of the 
terms, but some of the more frequently used terms are explained 
more fully in the following paragraphs. 
Leaves .—A typical, complete leaf (pi. II, fig. A) consists of three 
parts: the more or less expanded portion which is called the blade, 
the stemlike portion which is called the petiole, and two little ap¬ 
pendages at the base of the petiole which are called stipules. In a 
very large number of cases the stipules are lacking and in many 
cases the petiole is also lacking. When the petiole is lacking and the 
blade is thus attached directly to the stem the leaf is said to be 
sessile. When the blade is all in one piece and undivided the leaf 
is a simple leaf, but if it is divided so that the leaf appears to have 
several blades instead of only one it is compound. These several 
parts of a compound leaf are called leaflets. Leaflets or the blades 
of simple leaves may be variously lobed or toothed, or their margins 
may be completely without teeth or lobes, in which case they are said 
to be entire. Some compound leaves, such as those of the rose or the 
elder, have a central axis like a feather, and the leaflets are attached 
along two sides of this axis. Such a leaf is said to be pinnate or 
pinnately compound (pi. II, fig. C). Others, such as the lupine, have 
the leaflets all attached to the end of the petiole and such a leaf is 
said to be palmate or palmately compound (pi. II, fig. B). These 
same terms, pinnate and palmate, are sometimes used to describe 
the arrangement of the veins of a leaf. 
There are several terms that are used to describe the general shape 
of a leaf, and it will be necessary for us to understand the more 
frequently encountered of these (pi. III). One of them is lanceo¬ 
late, or lance-shaped, which refers to a leaf that is rather long, widest 
near the base and gradually tapering to a rather long tip, like a 
spearhead. Another much-used term is linear, which refers to a 
leaf that is uniformly narrow and with parallel edges like a grass 
leaf. Only a little less frequently used are the terms ovate, oval, 
and elliptical. Ovate is like a longitudinal section through an egg 
with the larger end downward, while oval and elliptical have exactly 
the same meaning that they have in geometry or in common language. 
Frequently the prefix ob- is used with lanceolate and ovate and 
means inversely. Thus oblanceolate means lance-shaped, but with the 
narrower part toward the base and obovate means inversely ovate. 
