''Cirsium rhothophilum'' is a rare
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
n species of
thistle known by the common name surf thistle. It is
endemic to
California, where it is known only from the coastline around the border between
San Luis Obispo and
Santa Barbara Counties. It grows in
sand dunes
A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, fl ...
and coastal scrub near the beach.
''Cirsium rhothophilum'' grows up to tall with fleshy, woolly herbage usually forming a mound. The thick leaves are wavy and covered in feltlike hairs. They may have smooth, lobed, or toothed edges and small spines. The largest leaves at the base of the plant may reach in length. The
inflorescence bears several clustered
flower heads
A pseudanthium (Greek for "false flower"; ) is an inflorescence that resembles a flower. The word is sometimes used for other structures that are neither a true flower nor a true inflorescence. Examples of pseudanthia include flower heads, compos ...
, each head up to 4 centimeters long and 6 cm wide. The heads are lined with woolly
phyllaries and filled with off-white to pale yellowish
disc florets but no
ray florets. The fruit is an
achene
An achene (; ), also sometimes called akene and occasionally achenium or achenocarp, is a type of simple dry fruit produced by many species of flowering plants. Achenes are monocarpellate (formed from one carpel) and indehiscent (they do not ope ...
a few millimeters long with a
pappus up to 2 centimeters in length.
Flora of North America, Surf thistle, ''Cirsium rhothophilum''
/ref>
References
External links
photo of herbarium specimen at Missouri Botanical Garden, collected in Santa Barbara County, isotype of ''Carduus maritima/Cirsium rhothophilum''Jepson Manual TreatmentCalphotos Photo gallery, University of California
rhothophilum
Endemic flora of California
Plants described in 1905
Flora without expected TNC conservation status
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