Lesson Plan: Rare Plants

Herbarium specimen of Aster nemoralis, a rare species
Three specimens of Aster nemoralis collected in the 1800s, mounted on a single herbarium sheet.

This exercise was revised by Sarah Taylor in 2020. If you know who created the original activity, please let us know! A pdf version of this activity is available here.

Some Connecticut plants are found less frequently now than they once were.

Below  is a list of such species. You can document the declines by going to the website of the University of Connecticut’s George Safford Torrey Herbarium and conducting a search for these species. Do not limit the search to Connecticut but obtain all specimens in the database.

After conducting the search, record the date on which each specimen was collected.







Then add up the number of specimens that were collected each decade since the first collection and plot the data.

Years Number of Records




You will not be able to generate a map for these species because the herbarium suppresses the precise location information. The herbarium does this because many of these species are on the state’s endangered species list, and it is important to discourage unscrupulous collectors, who might otherwise want to collect these rare plants. Some of the world’s most beautiful plants are threatened with extinction because collectors harvested so many of the plants growing wild to sell them to gardeners.

After plotting the data, get information on the species from the Plants database (or other web sites; the Plants database also will tell you the common name of your plant). Look especially for information that might help explain why the species is less widespread than it once was.


1.Is this a species that has, in fact, declined over time?


2. Is this a species that apparently always has been rare in Connecticut? 


3. If this species has declined in frequency over time, give three reasons that might account for the decline.


4. What else might account for changes in the number of specimens that have been collected? In other words, can you think of situations in which a species might not actually decline in frequency but in which there would be fewer specimens collected, giving the appearance of a decline? 


5. Are there species here that don’t appear to be rare at all and possibly should be considered for removal from the state’s endangered species list?


Species list

Abies balsamea
Alopecurus aequalis
Anemone canadensis
Arethusa bulbosa
Aristida longespica
Aristida purpurascens
Asplenium montanum
Aster nemoralis
Aster radula
Aster spectabilis
Betula pumila
Botrychium simplex
Cirsium horridulum
Corydalis flavula
Cryptogramma stelleri
Cypripedium acaule
Cypripedium arietinum
Cypripedium parviflorum
Cypripedium reginae
Deschampsia caespitosa
Dicentra canadensis
Diospyros virginiana
Diplazium pycnocarpon
Dryopteris campyloptera
Dryopteris goldiana
Equisetum palustre
Equisetum scirpoides
Eupatorium album
Hudsonia ericoides
Hudsonia tomentosa
Isotria medeoloides
Krigia biflora
Ledum groenlandicum
Lipariss liliifolia
Liquidambar styraciflua
Lycopodium selago
Lygodium palmatum
Malaxis monophyllos
Malaxis unifolia
Megalodonta beckii
Morus rubra
Oxalis violacea
Pinus resinosa
Platanthera blephariglottis
Platanthera ciliaris
Platanthera dilatata
Platanthera flava
Platanthera hookeri
Platanthera orbiculata
Polymnia canadensis
Potentilla arguta
Sagittaria subulata
Scutellaria integrifolia
Thuja occidentalis
Vitis novae-angliae


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