Timed plant identification
The student is handed two or three unknown specimens and a clock. Working against time, they open a dichotomous key and read the first couplet, check the diagnostic feature against the specimen, and follow the branch to the next couplet — observing venation, leaf arrangement, flower parts, or seed structure as each step demands. At the end they name each specimen’s taxon and justify it from the couplets they followed. There is nothing to copy and no key to consult beyond the one they’re working: the specimens are real, the time is real, and the identification has to hold up.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Systematic keying | Reads couplets at random or skips ahead, and loses track of which specimen is which. | Has a rough approach but skips a couplet or backtracks inefficiently. | Works the key couplet by couplet in order, letting each observation decide the next step, and tracks every specimen without confusion. |
| Diagnostic-feature observation | Cannot find the feature a couplet asks for, or misreads it — opposite vs. alternate leaves. | Reads obvious features but hesitates on close calls like pinnate vs. palmate venation. | Locates and reads each diagnostic feature confidently — leaf arrangement, venation, flower symmetry, margin type — even when it is subtle. |
| Couplet reasoning | Picks a branch without checking the specimen; cannot say why. | Chooses the right branch most of the time but misreads a couplet or a term. | Reads each couplet, tests both options against the specimen, and takes the branch the evidence supports — explaining each choice. |
| Handling & technique under time pressure | Rushes, damages specimens, or mixes them up as the clock runs. | Generally careful but gets sloppy under time — loses a specimen’s place in the key or handles it roughly. | Stays deliberate under pressure: specimens kept in order, features checked with a hand lens, nothing damaged, the key worked cleanly throughout. |
| Identification & justification | Names a taxon the couplets do not support. | Names the specimen but cites only one couplet, or hedges between two taxa. | Names each specimen’s taxon and justifies it by chaining the couplets and diagnostic features into a single conclusion. |
“The leaves are opposite and the venation is palmate, so at couplet four I went left, not right — that ruled out the alternate-leaved family. The flower parts in fives confirmed it before I committed to the ID.”
“It’s some kind of leafy plant. I followed the key partway but I wasn’t sure which feature the couplet meant, so I’d have to guess the rest.”
This assessment is AI-proof by design: it happens at the bench, with real specimens, against a real clock. No chatbot can turn a leaf to check its venation, follow a couplet on a plant it cannot see, or decide the next branch while the timer runs. The specimens differ from student to student, so there is no answer to look up — mastery is shown by keying and justifying in person, not by submitting.