HIGHER LAND PLANTS 



171 



alternate or opposite primary branches to the margin. 

 Palmate venation consists of several central, main 

 veins that fan out from a point at the base of the leaf 

 blade, each main vein usually being pinnately veined. 

 Parallel venation shows either many main parallel 

 veins running from the leaf blade base to apex, or 

 many main veins arching from the base (and perhaps 

 from a short, large vein that originates from the base) 

 to the apex. 



Megaphylls usually consist of three main parts. 

 The expanded part of the leaf is the terminally lo- 

 cated blade. The blade is often connected to a node 

 by a stem-like leaf structure, the petiole. Regularly 

 near the base of the petiole, there is one, perhaps two, 

 blade-like structures, the stipules. 



The structure of leaves, especially megaphylls, 

 often is important in the identification of individual 

 kinds of plants. So that the reader may obtain some 

 idea of structural diversity, and also as an aid to use 

 of plant identification manuals, the form of leaves as 

 to margins, outlines, bases, apices, and general or- 

 ganization is presented (Figure 11.4). 



The following types of leaf margins can be recog- 

 nized: entire, even and continuous, not cut or divided 

 in any way; undulate, slightly wavy; sinuate, strongly 

 wavy; serrate, saw-toothed, the "saw points" being 

 nearest to the leaf apex; serrulate, finely saw-toothed; 

 doubly serrate, saw-toothed pattern superimposed upon 

 a larger saw-toothed pattern, generally serrulate upon 

 serrate; dentate, pointed-toothed, the points generally 

 being at the center of the "tooth" and not directed 

 toward the leaf apex; denticulate, slightly and finely 

 toothed; crenate, rounded-toothed; cremdate, finely 

 rounded-toothed; incised, deeply and sharply cut or 

 slashed, commonly double serrate to an extreme; 

 lobed, typically steep but wave-like or finger-like cuts, 

 cuts less than halfway to the midrib of the blade (pin- 

 nate) or less than halfway to the point of origin of the 

 palmate veins that course down the middle of each 

 lobe (palmate); palrnately lobed, lobes radiate from a 

 common point normally at the base of the blade; pin- 

 nately lobed, lobes arranged oppositely or alternately 

 along the single midvein of the blade; parted, deeply 

 cut, incised, or lobed more than half way, either pal- 

 rnately or pinnately; divided, parted completely to the 

 base; compound, a step beyond divided, separated parts 

 palrnately or pinnately arranged leaf-like structures 

 (leaflets) having blade-like and petiole-like parts; 

 leaflets, can have any of the margins found in leaves; 



decompound leaves, leaves that are compounded two or 

 more times. 



Although leaves are simple, compound, or decom- 

 pound, decompound leaves are often considered in 

 more detail. Leaves that are twice compounded are 

 usually recognized as being bipinnate. Those that are 

 three times compounded are usually tripinnale. The 

 limits of a single leaf are diagnosed by the site of the 

 axillary bud. 



The following types of leaf outlines usually are 

 recognized : xca/^-Mf, regularly small and triangular; 

 linear, needle-like or long and quite narrow; oblong, 

 longer than broad but with parallel sides, similar to 

 linear but broader; elliptical, like a flattened circle 

 but with pointed apex and base; oval, broadly ellipti- 

 cal, with rounded apex and base; ovate, egg-like, 

 broader at the base than at the apex, both ends 

 rounded; lanceolate, like ovate, but the apex is drawn 

 out into a point; auriculate, with the base having a lobe 

 on each side of the midrib ("eared"); cordate, heart- 

 shaped with broader part toward the base and the 

 cleft of the "heart" inserted in the petiole; cuneate, 

 wedge-shaped, triangular with the triangle base at the 

 leaf apex and the triangle apex at the leaf base; obo- 

 vate, like ovate, but the broader part is at the apical 

 end; obcordate, like cordate, but the broader part and 

 cleft are toward the apex; oblanceolate, like lanceolate, 

 but the point is inserted into the petiole; spatulate, 

 apical part oblong but basal part narrower; and 

 reniform, kidney shaped. Often more than one of the 

 above terms is required to describe leaf outlines. 

 Such compound descriptive terms frequently are hy- 

 phenated (e.g., oblong-ovate). 



The following types of leaf bases often are men- 

 tioned in plant keys: rounded; auriculate: sagittate, ar- 

 row-like, generally appearing in a lanceolate leaf in 

 which a triangular portion of the base is missing; 

 hastate, arrow-like but the basal lobes are turned 

 outward; oblique or unequal, slanting, the portions of 

 the blade on either side of the midrib do not meet at 

 the same point; and cuneate, wedge-shaped. The 

 terms sagittate and hastate, like auriculate and 

 cuneate, often are applied to leaf outlines as well as 

 leaf bases. 



The common types of apices are as follows: acumi- 

 nate, gradually tapering to a point; acute, sharply 

 angled and pointed, not tapering; obtuse, rounded to 

 bjunt; mucronale, generally obtuse but with a slight 



