Now for the copyright attorneys out there I've made some modifications to Britton & Rose's key so keep your subpoenas to yourself. I've translated phrases like “transversely sulcate” or “less campanulate” into words that most of our dear readers can understand and use. I realize this isn't the easiest format to read but I couldn't figure out a good way to do this using HTML, any suggestions would be greatly appreciated. (Maybe there's a Java programmer out there...C'mon, it's just a bunch of nested “if...thens”!) Anyway, without further ado, the key to the Trichocereus species:

STEP 1

Are the stems basically erect and “more or less” branched? If yes, go to Step 1.1

Are the stems “simple”, low to the ground and growing in clusters? Go to Step 2.1

STEP 1.1

Are the limbs of the flower broad? Go to Step 1.1.1

Are the limbs of the flower narrow? You have a TRICHOCEREUS FASCICULARIS (aka Weberbauerocereus fascicularis).

STEP 1.1.1

Are the joints relatively slender, 2 to 3.5” (5 to 9cm.) thick? Go to 1.1.1.1

Are the joints stout (sturdy)? Go to 1.1.1.2

STEP 1.1.1.1

Are the ribs scored by longitudinal furrows between the areoles? Go to 1.1.1.1.1

Are the ribs NOT scored by longitudinal furrows between the areoles? Go to 1.1.1.1.2

STEP 1.1.1.1.1

Are the tubercles (small knobby projections) prominent? You have TRICHOCEREUS THELEGONUS.

Are the tubercles (small knobby projections) NOT prominent? You have TRICHOCEREUS THELEGONOIDES.

STEP 1.1.1.1.2

Is there only one central spine? You have TRICHOCEREUS SPACHIANUS.

Are there 4 central spines? You have TRICHOCEREUS LAMPROCHLORUS

STEP 1.1.1.2

Are the ribs on old plants very numerous and the spines bristle-like? You have TRICHOCEREUS PASACANA (or Helianthocereus pasacana).

Are there 4-17 ribs? Go to 1.1.1.2.1

STEP 1.1.1.2.1

Are the spines slender, .4 to 2.75” (1 to 7cm.) long? Go to 1.1.1.2.1.1

Are the spines very stout and “formidable”? Go to 1.1.1.2.1.2

STEP 1.1.1.2.1.1

Are there 4 to 9 ribs? Go to 1.1.1.2.1.1.1

Are there 16 or 17 ribs? You have TRICHOCEREUS CHILOENSIS (aka TRICHOCEREUS CHILENSIS).

STEP 1.1.1.2.1.1.1

Are the spines yellow, at least when young; are there 4 to 8 ribs? You have TRICHOCEREUS BRIDGESII.

Are the spines brown from the first: are there 6 to 8 ribs? Go to 1.1.1.2.1.1.1.1

STEP 1.1.1.2.1.1.1.1

Is the plant dark green; are the spines few or wanting at each areole? You have TRICHOCEREUS PACHANOI.

Is the plant light green; are there several spines at each areole? Go to 1.1.1.2.1.1.1.1.1

STEP 1.1.1.2.1.1.1.1.1

Are the spines shaped like a needle and up to 1” (2.5cm) long or less? You have TRICHOCEREUS MACROGONUS.

Are the spines linear and tapering to a fine point, up to 2.75” (7cm.) long? Go to 1.1.1.2.1.1.1.1.1.1

STEP 1.1.1.2.1.1.1.1.1.1

Are the spines swollen at the base, is young growth green? You have TRICHOCEREUS CUZCOENSIS.

Are the spines NOT swollen at the base, is young growth lighter, having a waxy/frosty appearance? You have TRICHOCEREUS PERUVIANUS.

STEP 1.1.1.2.1.2

Are the spines dark brown? You have TRICHOCEREUS COQUIMBANUS.

Are the spines yellow? You have TRICHOCEREUS TERSCHECKII.

STEP 2.1

Are the flowers short, red or yellow and more or less bell shaped? You have TRICHOCEREUS HUASCHA (aka Helianthocereus huascha).

Are the flowers elongated, funnelform, white? Go to 2.1.1

STEP 2.1.1

Is the tube longer than the limb, are there 12 to 18 ribs? Go to 2.1.1.1

Is the tube about the length of the limb? You have TRICHOCEREUS SCHICKENDANTZII.

STEP 2.1.1.1

Is the stem slender, elongated? You have TRICHOCEREUS STRIGOSUS.

Is the stem stout, short? You have TRICHOCEREUS SHAFERI.