Terminal bud and lenticels on Pop Ash (Fraxinus caroliniana), Florida.
Lateral buds (axillary buds) on pop ash. The leaves have fallen, with leaf scars just below (to the left of) the buds. Lenticels are conspicuous.
Axillary thorn (axillary bud grew into a thorn) on citrus
Brussels sprouts are giant axillary buds.
Taproots and Fibrous Roots
Fibrous roots on Eriocaulon decangulare, a Monocot (by John Bradford)Taproot on pouzol weed (Pouzolzia zeylanica), a Dicot.
Specialized stem types
A bulb is a thin stem surrounded by layered thick leaf bases, as in an onion.
A corm is a short thick stem at ground level. It looks like a bulb but is all stem.
A rhizome is a horizontal stem, usually underground. It looks like a root but has stem structure, including axillary buds.
A stolon is an above-ground rhizome, or “runner.”
A tuber is an extra-thick underground stem.
Liatris corm
Onion bulb: thin stem in layers of thick leaf bases
Tuber on Quercus virginiana, by John Bradford
Rhizome, the horizontal stem, with vertical stems rising along it. Paspalum vaginatum, by John Bradford
Stipules
Stipules are usually paired, as are the two long pointed upright triangular stipules at the photo center. The (compound) leaf with 4 leaflets visible is bent to the left, and the stem is tilted to the right. The axillary bud is hidden between the two stipules. The petiole to the left has an extrafloral nectary on it.Two two stipules on the base of a rose leaf, fused to the petiole.Sometimes stipules form a fringe (on Mexican-clover, Richardia grandiflora). Incidentally, nice example of hispid pubescence. The elliptic green growth tilted left behind the fringed stipule is an axillary bud beginning to grow out.Members of the coffee family have one stipule between the opposite petioles, as on this firebush (Hamelia patens). The stipule is the tail-shaped redish organ rising between the two petioles.Some plants (red mangrove, magnolias, figs) have a single stipule formed into a dunce-cap cover over the apical bud. This is strangler fig (Ficus aurea).These stipules are paired, one on either side of the light tan leaf scar. They are modified as thorns in this candelabra-cactus (Euphorbia lactea). See further commentary below in the caption of the cactus areole.Ouch! Paired stipules attack.In a true cactus such as this, the spine cluster (areole) is the axillary bud. The lowermost spine is the leaf whose axillary bud is the areole. The candelabra cactus above is not a true cactus, as evidenced by its stipular spines instead of the cactus areole.
Pubescence (= hairs)
Glabrous = hairless. Incidentally, these Nasurtium leaves are peltate.Tomentose = fuzzy, like felt (Rubus sp.)Hispid = bristly
Compound and lobed leaves
A compound leaf looks like a stem with leaves on it, but the axillary bud is at the base of the entire unit. The “leaves” on a compound leaf are leaflets with no axillary buds of their own. A pinnately compound leaf has the leaflets along a stalk (rachis). A palmately compound leaf has the leaflets radiating. If a leaf is not cut all the way into separate leaflets, it is pinnately or palmately lobed, that is, there is a web of leaf tissue between the lobes. Click on the thumbnails to enlarge them.
Palmately compound leaf. The leaflets radiate like spokes. Incidentally, note the classic paired stipules at the base of the petiole.
Palmately compound leaf
Palmately lobed
Pinnately compound leaf.
Even-pinnate = paripinnate
Twice pinnately compound
Trifoliate leaf. A trifoliate leaf has three leaflets.Virginia creeper (Parthenocissus quinquefolia) has palmately compound leaves. At the end of the branch, note the tendrils. Tendrils are stingy, twisty organs to allow some vines to grab hold.
Virginia creeper clinging to concrete wallVirginia creeper has beautiful tendrilsVirginia creeper tendrils end in sticky pads. The glue is a mix of pectins which becomes lignified.Tendrils on Smilax
Leaf Arrangements
One leaf per node = alternate
Two leaves per node = opposite
Three or more = whorled
Alternate leaves = one leaf at a time along stem
Opposite leaves. Leaves attached 2-by-2, in pairs, are opposite leaves.
Whorled leaves. Leaves are whorled when 3 or more at each node.
Leaf Shapes
Cordate is heart-shaped. The margins are entire on this glabrous leaf.Sagittate is shaped like an arrowhead.Lanceolate. Shaped like a lance tip, a candle flame. A long tapered tip is acuminate (ah-CUUM-ah-nate).Oblanceolate is upside-down lanceloate, widest above the middle.Ovate is similar to lanceolate but broader, egg-shaped. These opposite ovate leaves have serrate margins. Rough surfaces are rugose.Obovate is upside-down ovate, widest above the middle., broader than oblanceolate.Peltate is shaped like a thumb tack, the stalk attached to the center. These leaves have a crenate (with dull rounded teeth) margin.A serrate margin has saw-teeth (angled toward the leaf tip). Note the stipules flanking the axillary bud.A dentate margin has teeth sticking straight out. The leaf tip here is obtuse (that is, a blunt angle).A mucronate leaf tip has a tiny tooth.An emarginate leaf tip has a notch.
Practice Quiz
1. Leaves attached two-by-two are:
A. Alternate
B. Opposite
C. Whorled
D. Paripinnate
2. A leaf margin resembling sawteeth is:
A. Serrate
B. Crenate
C. Sinuous
D. Pinnate
3. A compound leaf where the leaflets radiate like spokes is:
A. Pinnately compound
B. Decompound
C. Palmately lobed
D. Palmately compound
4. Fuzzy like felt:
A. Hispid
B. Hirsute
C. Peltate
D. Tomentose
5. Heart-shaped:
A. Hastate
B. Sagittate
C. Cordate
D. Hearty
6. Hairless:
A. Glabrous
B. Nodose
C. Nudate
D. Hirsute
7. Roots along the stem above the ground:
A. Fibrous
B. Lianate
C. Adventitious
D. Stolons
8. Shaped like a thumb tack:
A. Tacky
B. Obovate
C. Saccate
D. Peltate
9. Another name for axillary buds:
A. Lateral buds
B. Terminal buds
C. Bundle traces
D. Leaf scars
10. Immediately above every leaf attachment:
A. Terminal bud
B. Lenticel
C. Axillary bud
D. Leaf scar
11. Paired outgrowths at petiole base:
A. Lodicules
B. Elaiosomes
C. Stipules
D. Lateral buds
12. Stem between leaf attachment points:
A. Interludes
B. Intrazones
C. Alamodes
D. Internodes
13. Leaf blade with notch at tip:
A. Clavate
B. Emarginate
C. Glaucous
D. Cordate
14. Leaf blade shaped like a candle flame:
A. Obovate
B. Lanceolate
C. Oblate
D. Flameous
15. Upside-down egg, widest above middle:
A. Obovate
B. Lanceolate
C. Elliptic
D. Dendritic
16. A leaf with leaflets along what looks like a stem (but the leaflets do not have axillary buds) is:
A. Palmately compound
B. Pinnately lobed
C. Ultracompound
D. Pinnately compound
17. Describe each leaf below. shape? Margin? Tip? Is it compound? Pubescence?
