Flora of North America species comparison

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Cirsium rhothophilum

surf thistle
Habit Biennials or short-lived, usually monocarpic perennials, 10–100 cm; taprooted with simple or branched caudices.
Stems

1–several, spreading to erect, bushlike or forming low rounded mounds, gray-tomentose with appressed feltlike trichomes;

branches 0–several, inclined to ascending, stiff.
Leaves

blades elliptic to ovate, 10–25 cm, strongly undulate, usually broadly pinnatifid, lobes entire or coarsely few-toothed or -lobed, main spines abrupt, 1–4 mm, faces gray-white-tomentose with appressed feltlike, non-septate trichomes;

basal present or withered at flowering, winged-petiolate;

principal cauline well distributed, winged-petiolate to sessile, gradually reduced, bases clasping with expanded auricles;

distal reduced, spines to 8 mm.
Peduncles

0–7 cm.
Involucres

hemispheric or campanulate, 3–4 × 4–6 cm, densely arachnoid.
Corollas

white to pale yellow, 20–34 mm, tubes 11–15 mm, throats 5–8 mm, lobes 5–8 mm;

style tips 3–4 mm.
Phyllaries

in 8–10 series, imbricate, linear, abaxial faces without glutinous ridge;

outer and mid bases short- appressed, margins spiny-ciliate, apices long, spreading to erect, spines straight, 2–5 mm;

apices of inner flattened or spine-tipped, serrate to scabrid, sometimes pectinately fringed.
Heads

1–many, erect, terminal on branches in subcapitate to congested, corymbiform arrays, closely subtended by clustered, ± leafy bracts.
Cypselae

light–brown to black, 5–7 mm, apical collars whitish, 0.2–0.3 mm;

pappi 15–25 mm.
2n

= 34.

Cirsium rhothophilum
Phenology Flowering mostly spring–summer (Apr–Aug), occasionally year round.
Habitat Coastal dunes and bluffs
Elevation 0–20 m (0–100 ft)
Distribution
from FNA
CA
[BONAP county map]
Discussion

Of conservation concern.

Cirsium rhothophilum is endemic to the dunes of southern San Luis Obispo and northern Santa Barbara counties. It rarely forms hybrids with C. occidentale var. occidentale and C. scariosum var. citrinum.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 19, p. 161.
Parent taxa Asteraceae > tribe Cardueae > Cirsium
Sibling taxa
C. altissimum, C. andersonii, C. andrewsii, C. arizonicum, C. arvense, C. barnebyi, C. brevifolium, C. brevistylum, C. canescens, C. carolinianum, C. ciliolatum, C. clavatum, C. crassicaule, C. cymosum, C. discolor, C. douglasii, C. drummondii, C. eatonii, C. edule, C. engelmannii, C. flodmanii, C. foliosum, C. fontinale, C. grahamii, C. helenioides, C. hookerianum, C. horridulum, C. hydrophilum, C. inamoenum, C. joannae, C. kamtschaticum, C. lecontei, C. longistylum, C. mohavense, C. muticum, C. neomexicanum, C. nuttallii, C. occidentale, C. ochrocentrum, C. ownbeyi, C. palustre, C. parryi, C. perplexans, C. pitcheri, C. praeteriens, C. pulcherrimum, C. pumilum, C. quercetorum, C. remotifolium, C. repandum, C. rydbergii, C. scariosum, C. texanum, C. tracyi, C. turneri, C. undulatum, C. vinaceum, C. virginianum, C. vulgare, C. wheeleri, C. wrightii
Synonyms Carduus maritima
Name authority S. F. Blake: J. Wash. Acad. Sci. 21: 336. (1931)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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