Cardamine douglassii

Purple Cress

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Family: Brassicaceae (Mustard family)

Mid-Atlantic bloom time: March - April
Mid-Atlantic fruit ripe: April - May

Identification Caution: Purple Cress (Cardamine douglassii) and Spring Cress (Cardamine bulbosa) are often nearly impossible to differentiate in the field. Many of their defining characteristics overlap, further complicated by them hybridizing in locations where they both can grow. Perhaps the most quoted source for their identification is a 1976 paper by Hart and Eshbaughi in the Journal of the New England Botanical Club1.

The identification characters most often used to separate the two species are:

feature C. bulbosa C. douglassii
rhizomes short, erect or horizontal, barely subterranean, stout, knotty or tuberous, white sometimes surficial and becoming green
stems 15–60 cm,erect, simple or with a few upper branches, glabrous, or with hairs < 0.1 mm long 10–50 cm, erect, pubescent (with hairs (0.2–) 0.3–0.6 (–0.8) mm long), with the lower portion cinereous (ash-colored)
basal leaves blades 2.5–8 cm, oval or rotund to reniform, entire or repand, rarely purplish beneath, deciduous before anthesis to 3 cm, orbicular or nearly so, purplish beneath, especially when in full sun, petiolate
cauline leaves 4–12, scattered, ovate or narrowly oblong to elliptic or lanceolate, serrate or entire and undulate 2–5, smaller, ovate to oblong
petioles to 9 cm on basal leaves, reduced progressively upward to lacking lowermost 2 cauline leaves sometimes petiolate, otherwise petioles lacking
pedicels to 4 cm, ascending to divergent lowermost pedicels 1.5–4 cm, divaricately ascending
sepals 2.5–5 mm 3–6 mm
petals 7–16 mm, white, or rarely, pink 7–20 mm, pink to lavender or, rarely, white
siliques 15–30 x to 1.5 mm, plus a beak 2–3 mm 10–20 x 1–2 mm, plus a beak 2–4 mm
seeds to 2.5 mm, dark brown to 1.5 mm, dark brown
bloom/fruit Mar–May; Apr–May Mar–Apr; Apr–May

The specimens shown here represent my best guess as to them being Purple Cress (C. douglassii), because their:
  - upper stems are pubescent
  - sepals are pubescent
  - near-basal leaves are flat
  - flowers are pink or purple, not mostly white



20 March 2022
Great Falls National Park, Great Falls, VA
27 March 2022
Great Falls National Park, Great Falls, VA
20 March 2022
Great Falls National Park, Great Falls, VA
(note pubescent stem)
20 March 2022
Great Falls National Park, Great Falls, VA
(pubescent stem)
3 April 2022
Great Falls National Park, Great Falls, VA
(ignore stick, note pubescent stem)
3 April 2022
Great Falls National Park, Great Falls, VA
(measuring pubescence on stem)
20 March 2022
Great Falls National Park, Great Falls, VA
(white-flowered specimen, but with pubescence; possibly hybrid)
1 May 2024
Great Falls National Park, Great Falls, VA
(siliques)
1 May 2024
(silique)
Great Falls National Park, Great Falls, VA
1 May 2024
Great Falls National Park, Great Falls, VA
(silique)
   


References

1:   Thomas W. Hart and W. Hardy Eshbaughi, "The Biosystematics of Cardamine bulbosa and C. Douglassii", Rhodora, Journal of the New England Botanical Club, Vol. 78, No. 815, pp. 329-419, July 1976 (accessed through https://www.jstor.org/stable/23311220)




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