| 1 | STAMENS & STYLE | Longer than the petals. | 17 |
| | Shorter than or equalling the petals. | 2 |
| 2 | FLOWER | With small asymetrical sepals. | 15 |
| | Flowers very small. | |
| | With symetrical sepals | 3 |
| 3 | PETAL | short, to 5cm long | 5 |
| | long, 9cm or more | 3A |
| 3A | PETAL | long, straplike, lax to hanging | 4 |
| | long, more or less erect | 3B |
| 3B | PETAL | with appendage | 3C |
| | without appendage, plant bulbose, | trigalensis |
| | inflo almost capitate | |
| | without appendage, plant funnel shaped | zarumensis |
| | inflo bipinnate, spikes 30cm long, petals | |
| | 13cm long | |
| 3C | PLANT | bulbose, petals to 14cm long with | boeghii |
| | appendage | |
| | funnel shaped, petals to 12cm long | drewii |
| | with appendage | |
| 4 | INFLORESCENCE | Simple. Floral bract longer than sepals | viridiflora |
| | Epiphyte | |
| | Compound. Floral bracts about equalling | macropetala |
| | sepals, Epiphyte | |
| | Compound. Floral bract shorter than sepals | grandis |
| | Lithophyte | |
| 5 | INFLORESCENCE | Simple. | 8 |
| | Compound. | 6 |
| 6 | LEAF SHEATH | Spreading on the stem making a funnel | 6A |
| | shaped rosette. | |
| | forming a tubular rosette, leaves to 40cm | cernua |
| | long, sheath very broad, almost as long as | |
| | the very narrow blade | |
| | Forming a spherical 7-11 cm high, secund | boqueronensis |
| | claw-like rosette. Blades 4-7 cm long | |
| | tapering to a long filiform tip | |
| | Forming a bulbose rosette. | 6B |
| 6A | SCAPE | 1 - 2 cm long, inflorescence sunk | mauryana |
| | in rosette, leaves white scaled | |
| | mauryana, with secund leaves | var secundifolia |
| | 1.5 - 3 cm long, inflor exceeds leaf rosette | teloloapanensis |
| | leaves grey scales | |
| | longer, inflorescence well above rosette | chontalensis |
| | Petals appendaged | |
| | longer, much exceeding the leaves, inflo | robusta |
| | digitate with few spikes, floral b purple | |
| | exceeding the sepala | |
| | to 60cm long, erect, inflo to 65 x 20cm, | yerbasantae |
| | with to 25 spikes | |
| 6B | LEAVES | Almost filiform | 7 |
| | to 3cm wide, inflorescence hanging, | bakiorum |
| | branches spreading | |
| | 3 cm wide, inflorescence hanging, | limonensis |
| | cylindric, petals appendaged | |
| 7 | INFLORESCENCE | On long stem, which is as long or longer than | plumosa |
| | the leaf. Leaf with white feathery scales. | |
| | stem shorter than leaf rosette, 5-8 cm long | caballosensis |
| | Leaf dense grey white frosty scales | |
| | abaxially dense felt-like | |
| | Almost sessile. Stem much shorter than | atroviridipetala |
| | and masked by the leaves. | |
| | Key to T. atroviridipetala | |
| | 1.Peduncle hardly visible 2 | |
| | 1a.Peduncle short 3 | |
| | 2. Caulescent - dense rosette 15x 12cm wide. | |
| | Inflorescence compound densely capitate | |
| | atroviridipetala var yagulensis | |
| | 2a. Stemless – a dense flattened rosette spikes– | |
| | mainly one flowered | |
| | atroviridpetala var atroviridipetala | |
| | 3. Short peduncle Leaf sheath – forming a | |
| | Bulb, with 2-6 spikes | |
| | atroviridipetala var. longepedunculata | |
| 8 | SCAPE | Long. | 10 |
| | Short. Inflorescence almost | 9 |
| | sessile. | |
| 9 | PLANT | Long filiform growth, similar to Beard Moss | usneoides |
| | Rosette growth.leaves to 15cm long, | lepidosepala |
| | floral bracts green | |
| | open rosette, leaves 4-7 cm long, floral | teloloapanensis |
| | bracta pink | |
| | secund rosette, leaves to 5cm long | penascoensis |
| | floral bracts intensive pink | |
| 10 | PETAL | appendaged, Flower dense distichous | chontalensis |
| | Spike sword-shaped | |
| | Not appendaged | 11 |
| 11 | FLOWER | Arranged dense distichously on | 13 |
| | rhachis. Spike short swordshaped | |
| | Arranged laxly on rhachis. Floral stem | ixioides ssp viridiflora |
| | hanging ca 5 flowers polystichous. | |
| | polystichous. Floral bract pink. | |
| 13 | PLANT | Base bulblike. | ignesiae |
| | Base NOT bulblike. | 14 |
| 14 | FLORAL BRACT | 2.5 cm long, pink grey scales. | tortilis |
| | Flower emerald green. | (ehrenbergii) |
| | 3.5 cm long, smooth yellowish. | lotteae |
| | Flower yellow green. | |
| 15 (2) | FLORAL BRACT | Longer than sepals. | R tenuispica |
| | Shorter than sepals. | 16 |
| 16 | SCAPE BRACT | Longer than the internodes. | Rparviflora v. expansa |
| | Small, barely half as long as the | commixa |
| | internodes. | |
| 17 (1) | INFLORESCENCE | .Compound. | 21 |
| | Simple. | 18 |
| 18 | FLOWER | polystichous, inflo fusiform to 9 x 3 cm | erubescens |
| | generally pendant, Floral bracts imbricate | (benthamiana) |
| | petals to 7 cm long | |
| | polystichous, inflo not fusiform to 7 cm | erubescens |
| | generally pendant, Floral bracts spreading | var patentibracteata |
| | petals to 5 cm long | |
| | polystichous, inflo narrower than 3cm | arroyensis |
| | pendent , petals to 7 cm long | |
| | polystichous, scape a little recurved not | quaquaflorifera |
| | pendent, Inflo 10cm x 3cm, petals to 5.5cm | |
| | long | |
| | distichous | 18A |
| 18A | INFLORESCENCE | Erect | 19 |
| | Hanging | 18B |
| 18B | INFLORESCENCE | 2 cm wide, floral bracts mainly lepidote | incurva |
| | petals to 3.6 cm long | |
| | 2cm wide, floral bracts glabrous, petals | penduliscapa |
| | to 6cm long | |
| | 3 cm wide, bent upwards in middle | curvispica |
| 19 | FLOWER | Arranged laxly on rhachis. | fresnilloensis |
| | Plant to 22 cm high, scape to | or karwinskyana |
| | 12 cm long | |
| | Arranged closely on rhachis. | 20 |
| | Inflorescence sword shaped. | |
| 20 | STAMENS | and style longer than petals | 20A |
| | included in petals, only style exceeding | petraea |
| 20A | LEAF | Green, not strikingly scaled. | cryptopoda |
| | Dense grey scaled. Spike 20cm x 1.5cm | achyrostachys |
| | Dense grey scaled, spike 7cm x 2cm | rayonesensis |
| | Dense grey scaled, Spike 16cm x 4cm | marabascoensis |
| 21 (17) | PLANT | With hanging inflorescence. | 21A |
| | with decurved scape, inflorescence dense | arpocalyx |
| | bipinnate, floral bracts red | |
| | With erect inflorescence. | 21D |
| 21A | SPIKE | Side spikes almost parallel | 21C |
| | Side spikes at right angles | 21B |
| 21B | SCAPE | 20 cm long, inflorescence to 10 cm long | alfredo-lauii |
| | 20cm long, inflorescence 30-80cm long | hromadnikiana |
| | spikes 12 x 2.5cm | |
| | 20cm long, inflo 25cm long, 38-40 spikes | supermexicana |
| | 10x4cm | v. pendula |
| | 50 cm long, inflorescence 30 - 60 cm long | prodigiosa |
| | spikes 9 x 5cm | |
| 21C | SPIKES | lax, floral bracts 35 mm long | pereziana |
| | petreziana but floral bracts 25 mm long, | pereziana v canescens |
| | strongly lepidote | |
| | rhachis not visible | 21E |
| 21D | PETALS | soon drooping, Inflo to quadripinnate | paniculata |
| | remaining fairly rigid | 21F |
| 21E | SCAPE | almost lacking to 25cm long, petals | zaragozaensis |
| | without appendage | |
| | 3 - 6 cm long, inflorescence 18 - 25 cm | incurva |
| | long, spikes long, floral bracts not keeled | |
| | 10cm long, Inflo 16cm long, Spikes 8cm | lutheri |
| | long, floral bracts keeled, top 3-4 bracts at | |
| | top of spike sterile | |
| | 17 - 21 cm long, inflorescence 24 - 30 cm | castaneobulbosa |
| | long, spikes long, floral bracts keeled | |
| | To 20 cm long, Inflorescence to 14 cm long | strobeliae |
| | spikes very short, to 3 cm long hidden by | |
| | the primary bracts which have wavy edges | |
| 21F | RHACHIS | zigzag angled | 21G |
| | straight to almost straight | 21H |
| 21G | FLORAL BRACTS | smooth and sepals smooth | limbata |
| | prominently nerved and sepals nerved | calcicola |
| | glabrous, green sometimes withpink edges | cucaensis |
| | inflorescence simple to once branched to | |
| | twice branched, peduncle and rhachis | |
| | salmon coloured | |
| 21H | PETALS | with appendage, green with violet speckles | cereicola |
| | spike narrow, to 15mm wide | |
| | without appendage | 22 |
| 22 | SPIKE | suberect, to 25, long and narrow to 30x2cm, | taxcoensis |
| | stipes 11-18 cm long, floral bracts densely | |
| | lepidote | |
| | suberect to 23, long & narrow, to 26 x 2.4cm | religiosa |
| | stipes 14-28 cm long, floral bracts mostly | |
| | glabrous, pruinose | |
| | erect, 8-16, long and narrow, to 30x1.5cm | zacualpanensis |
| | sub-cylindric, 3.5 -5.7 cm long, 2-5 flowers | fascifolia |
| | floral bracts orange, ca equalling sepals | |
| | Sword shaped. | 22A |
| 22A | RHACHIS | visible, leaf rosette narrow funnel form | suesilliae |
| | Not visible | 23 |
| 23 | SCAPE | Short, not taller than the leaf rosette | cryptopoda |
| | one or two spikes, petals yellow-green | |
| | short, about equalling rosette, 7 - 13 | mixtecorum |
| | spikes, petals yellow-green | |
| | as long as leaf rosette, 15-30 spikes, floral | celata |
| | bracts red, exceeding sepals glabrous only | |
| | at top, petals yellow green | |
| | To 20cm long inconspicuous hidden by | borealis |
| | leaves 16-30 spikes | |
| | Long, or exceeds the leaf rosette. | 23A |
| 23A | PRIMARY BRACT | Hides bottom spikes. Petal yellow green | 23B |
| | Narrow, longer than the bottom spikes | marceloi |
| | does not hide bottom spikes. | 24 |
| 23B | INFLORESCENCE | 30 to 45 cm long. Primary bracts pink | cossonii |
| | long attenuate | |
| | 20-30cm long, primary bracts pink | lomae-blancae |
| | short attenuate | |
| | to 20cm long, primary bracts red, long | macrochlamys |
| | attenuate, spikes erect | |
| | To 17cm long. Primary bracts pale green | carlos-hankii |
| | beneath reddish above, long attenuate, | |
| | spikes spreading | |
| | To 15 cm long, primary br. rose, petals | sierrahalensis |
| | 5 cm long | |
| 24 | FLORAL BRACT | glabrous,shiny green to yellowish green. | 24A |
| | glabrous, shiny red | jalisco-pinicola |
| | Grey scaled. | 24B |
| 24A | INFLORESCENCE | to 70cm long, with up to 40 spikes, primary | supermexicana |
| | bracts long linear, more than 1/2 the | |
| | bottom spikes | |
| | supermexicana but inflor compact | supermexicana |
| | cylindric, posterior sepals 5 mm connate | var. saxicola |
| | To 25 cm long with up to 8 spikes, primary | roland gosselinii |
| | bracts much shorter than the spikes | |
| | to 25cm long, with up to 5 digitate spikes | macvaughii |
| | primary bracts 2.5cm long, petals greenish | |
| | white | |
| | to 25cm long, with up to 8 spikes, primary | hintoniana |
| | bracts large but not as long as the spikes | |
| | To 10cm long with mainly 4 but up to 6 spikes | rothii |
| 24B | PRIMARY BRACT | Broadly oval shaped with the bottom | bourgaei |
| | ones having a long awllike tip.Inflo to 30cm | |
| | long, acute floral bracts equal sepals, | |
| | sepals lepidote | |
| | broadly oval shaped with the bottom ones | takizawae |
| | having a long awl-like tip, inflo 25-80cm | |
| | long, floral bracts acuminate with filiform | |
| | tip equalling the sepals, sepals nearly | |
| | glabrous | |
| | Broadly oval shaped with the bottom | nuyooensis |
| | ones having a long awllike tip.Inflo to 60cm | |
| | long, floral bracts longer than sepals | |
| | With no long awllike tip. | 24C |
| 24C | SCAPE | To 20 cm long. Floral bract green with | schusteri |
| | scaled red top. | |
| | To 55 cm long. Floral bract pink, grey scaled | roseoscapa |
(D) PETAL - GREEN