2 1 Areoles bearing glochids; stems jointed, cylindric or flattened, not ribbed, not bearing prominent tubercles.  3

Areoles not bearing glochids; stems cylindric, sometimes bearing joints, ribs or prominent tubercles. 16

3 2  Joints cylindric; spines sheathed when young: Chollas 4

Joints flattened (pads), spines not sheathed 9

4 3  Lateral joints ¼” in diameter, 1-3” long; Plant bushy 

Lateral joints ½” or more in diameter, over 3” long 5

5 4 Branchlets ¾” or more in diameter, bearing elongate, low tubercles    6

Branchlets to ½” in diameter, smooth or bearing obscure tubercles; plant arborescent at maturity

6 5 Branches in whorls; plants arborescent 

Branches not in whorls; plants sometimes arborescent 7

7 6 Plants arborescent, much branched; spines straw-colored 8

Plants sprawling shrubs, loosely branched; spines dark to light, but not straw-colored

8 7 Plants to 6’ tall; terminal joints short, very easily dislodged; fruits not in chains
 

Plants to 12’ tall; terminal joints longer, not as easily dislodged; fruits persisting in chains (variety with fewer and shorter spines on more prominent tubercles is mammillata

9 3 Joints broad, flattened, alternate or irregularly arranged; Prickly Pears 10
Joints narrow, flattened, whorled 

10 9 Joints 3-4 times longer than wide, tapering to a long slender tip

Joints not more than twice as long as wide, orbicular to obovate 11

11 10  Central spines present, stout, whitish or yellowish

Central Spines, if present, not stout, yellowish to reddish 12

12 11 Plants arborescent, with distinct trunks 13

Plants shrubs, not with distinct trunks 15

13 12 Pads very thick; glochids few, scarcely visible; areoles widely spaced
 

Pads less than ¾” thick; glochids numerous, obvious; areoles closely spaced 14

14 13 Pads about ½” thick, green to blue-green

Pads about ¼” thick, green turning purplish during cold or dry seasons

15 12 Plants to 1 ½’ tall, mostly one joint high; joints obovate, gray, wrinkled, with abundant red glochids

Plants to 4’ tall, several joints high; joints oblong to orbicular, green, velvety, with abundant red to white glochids 

16 2 Stems weak, arching or trailing, with long slender joints 17

Stems erect 20

17 16 Stems gray, angled with 3-6 prominent longitudinal ribs bearing blackish spines less than 1/8^” long

Stems green (or purplish), ribbed but not angled; spines white or yellow to gray, more than ¼” long 1 ??

18 17 Spines ½” (or less) long; ribs not prominent

Spines 1” long or longer; ribs prominent 19

19 18 Older stems approximately 3” in diameter, turning red during cold or dry periods, branching near the base

Older stems approximately 2” in diameter, green, branching above the base

20 16 Stems columnar, 6’ or more tall, ribbed; spines terete, straight (in one form absent) 21

Stems less than 6’ tall, or if more, then at least certain spines definitely curved and flattened 23

21 20 Plant branching well above the constricted base

Plant branching near the unconstricted base, sometimes also above 22

22 21 Ribs numerous, 12-17; spines uniform throughout plant

Ribs fewer, 5-7; spines not uniform throughout plant; mature branch tips with areoles bearing numerous flexuous spines(or spines absent; areoles few; rounded protruberences forming irregular ribs in forma monstrosus) 

23 20 Plants with prominent tubercles not arranged in longitudinal ribs 24

Plants with longitudinal ribs 25

24 23 Tubercles grooved above; central spine straight

Tubercles not grooved; central spine hooked

25 23 Spines straight or slightly curved, but not hooked or distinctly twisted 26

At least some of the spines hooked or distinctly twisted 28

26 25 Plants cylindric, branching mostly at or below soil line

Plants globose, solitary or branched at base or above 27

27 26 Spines terete, dark-colored; plants often branched above base, apex not depressed, not woolly

Spines flattened, golden yellow; plants solitary or branched at base; apex depressed, woolly

28 25 Plants nearly as wide as tall; central spines not twisted, sometimes hooked 
 

Plants much taller than wire; central spines twisted, often hooked

29 1 Plants palms or palm-like (some without trunks) 30

Plants not palm-like 53

30 29 Leaves palmately veined;  Fan Palms 31

Leaves pinnately veined; Feather Palms 43

31 30 Trunks clustered, usually dward to 10’ tall, often hidden in foliage 32

Trunks solitary, of various heights 33

32 31 Blades deeply divided into 5-10 segments, almost as leaflets (appearing like dwarf bamboo); petioles not armed or irregularly so

Blades not deeply divided to appear as leaflets; petioles distinctly armed with teeth

33 31 Palms dwarf; trunk to 4’ tall; blades deeply divided into two equal parts, each with minor divisions; petioles not armed

Palms not dwarf; trunks to 10’ or more tall; blades not deeply divided into two parts; petioles armed or not 34

34 33 Midvein decidedly curled downward and backward; petiole not with marginal teeth 35

Midvein little or not at all curled downward and backward; petioles with or without marginal teeth  36

35 34 Leaf blades to 6’ across; inflorexcence shorter than petiole; fruit about ½” in diameter

Leaf blades to 4’ across; inflorescence longer than petiole; fruit about 3/8” in diameter. 

36 34 Very long, stout spines terminating stiff network of old leaf sheaths.

No stout spines terminating old leaf sheaths 37

37 36 Leaf blades with sharply drooping segments Fountain Palms 38

Leaf blades not with sharply drooping segments 39

38 37 Trees to 60’ tall; leaves soft green; petioles armed.

Trees to 30’ tall; leaves bright shiny green; petioles sometimes armed.  

Petiole smooth (or with few small teeth at base) 

Petiole with marginal teeth 40

Petiole with very fine teeth; trunk with very many hair-like fibers.

Petiole with coarse teeth; trunk not with very many hair-like fibers (though some may be present) 4 ??

Leaves blue-glaucous. 

Leaves green or gray-green 42

42 41 Trunks short to medium height, stout, about 2’ or more in diameter at middle; blades very filiferous at maturity

Trunk tall, slender, about 1’ in diameter at middle; blades little filiferous.

Leaves flat or folded lonitudinally in bud; pinnae not with revolute margins 44

Leaflets not with a prominent midvein Dioon edule

Lower pinae not developed into spines 48

Trunks solitary, not dwarf 47

Leaves white floccose in interrupted lines on ribs beneath

Leaves not white floccose beneath 

Trees slender to 100’ tall, with a rather dense crown of green to bluish green leaves, often glaucous; fruit cylindric, 1-2” long, edible; seed more than 3 times longer than wide

Trees stout, to 60’ tall, with a dense crown of green to light green leaves;, fruit about ¾” long, not considered edible; seed less than 3 times longer than wide

48 44 Pinnae tips erose (jagged); leaflets rigid, many-veined, broadened at apex.

Pinnae tips pointed, not erose; leaflets various 49

49 48 Leaves blue-glaucous, arching, petiole spiny at base.

Leaves green; petiole not spiny 50

50 49 Shrubby trees to 8’ tall; pinnae to 20 pairs in number 

Trees 20-50 feet or more tall; pinae many, 40 pairs or more 51

51 50 Petiole fibrous shaggy 

Petiole not fibrous shaggy 52

52 51 Pinnae with lateral veins prominent above, chaffy on midvein and margins beneath, at least when young; stems branching at maturity; leaf rachis yellow to red beneath. 
 

Pinnae with lateral vines prominent beneath, coarsely chaffy on only midvein beneath; leaf rachis slightly grayish beneath; stems not branching.

53 29 Plants grasses (including bamboos) or grass-like; leaves parallel veined, ensheathing stems 54

Plants not grass-like; leaves various but not parallel veined and ensheathing stems. 67

54 53 Plants aquatic or semiaquatic; leaves strongly ascending; Cattails

Plants terrestrial; leaves not strongly ascending 55

55 54 Culms(stems) terete, jointed, or various heights; all leaf sheaths with blades, these sometimes deciduous 56

Culms angled slightly, but not jointed, 2-4' tall, stout, bearing many long, firm, spreading leaves at the apex (like umbrella ribs); basal leaf sheaths bladeless

56  55 Blades much broader than the sheath, stalked, deciduous from the joint at sheath; sheaths sometimes persistent Bamboos 57

Blades narrower than or as broad as the sheaths, not stalked; blades and sheaths persistent 65

57 56 Culms flattened on one side above the node 58

Culms terete throughout 60

58 57 Culms becoming black

Culms becoming yellow or golden 59

59 58 Culms flattened on one side above node

Culms grooved on one side above node

60 57 Culms to about 3' tall, from running rhizomes, not clumping 61

Culms 5' or more tall, sometimes in dense clumps 62

61 60 Internodes solid, short; culms to 1 foot tall, purplish

Internodes hollow, long; culms to 3' tall(leaves green or variegated)

62 60 Rhizome internodes with many scattered roots developing; culms with several branches at a node; sheath bristles stiff, scabrous 63

Rhizome internodes with a single band or row of roots developing; culms with one or two branches at a node; sheath bristles flexuous, not scabrous

63 62 At least some internodes swollen in the middle (intensifies if pot-bound)

Internodes not swollen in the middle 64

64 63 Stems to 60' or more tall, 2-4" in diameter at maturity, deep green

Stems to 35' tall, 1" in diameter, often striped green, yellow or pink

65 56 Leaf margins finely serrate (serrulate) 66

Leaf margins entire, smooth

66 65 Culms 18-36" tall, less than 1/8" in diameter, scabrous below the inflorescence; inflorescence narrow, to 12" long

 
Culms 4-20' tall, about 1/4" or more in diameter, glabrous throughout; inflorescence open, plume-like, to 2' long Cortaderia selloana

67 53 Plants yuccas or yucca-like, often scapose; leaves in a rosette, basal or atop a trunk (occasionally well distributed along trunk in young plants), often linear, sometimes succulent 68

Plants neither scapose nor with a rosette of leaves 77

68 67 Leaves with marginal prickles 69

Leaves not with marginal prickles, but sometimes finely serrate (serrulate) 71

69 68 Leaves very succulent, usually spotted with a lighter color; no fibers in center of leaf; basal rosette to 2' in diameter Aloe spp.

Leaves not succulent or succulent fibers in the center of the leaf; basal rosette usually larger than 2' in diameter 70

70 69 Blades thin, to 1" wide, about 3' long, tapering to long foliaceous tips; margins bearing numerous tiny recurved prickles

Blades thick, succulent, with strong central fibers, to 6" or more wide, about 4' long, with stout spines at tips; margins bearing relatively few but large prickles (variety with white or yellow margined leaves is marginata)

71 68 Leaf margins serrulate to entire 72

Leaf margins filiferous 75

72 71 Leaves rigid, dagger-like 73

Leaves flexible, lower leaves recurved or drooping 74

73 72 Leaves to about 8" long, about 1/2" wide; arborescent, much branched Yucca brevifolia

Leaves to about 1' or more long, about 3/4" or more wide; sometimes arborescent, little branched Yucca aloifolia

74 72 Arborescent, stems often with swollen bases; leaf margins sharply serrate Yucca elephantipes

Stems short, not noticeably swollen at bases; leaf margins entire or irregularly serrulate to undulate Yucca recurvifolia

75 71 Plants at maturity with trunks; leaf blades flat, narrow, with many fine fibers Yucca elata

Plants at maturity not with trunks, or if so, then not erect; leaf blades concave, narrow to broad, with few and coarse fibers 76

76 75