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Centaurea stoebe ssp. micranthos

Centaurea stoebe L. ssp. micranthos (Gugler) Hayek

Acosta maculosa auct. non (Lam.) Holub

Centaurea biebersteinii DC.

Centaurea maculosa auct. non Lam.

Spotted Knapweed

KingdomPlantaePlants, but not fungi, lichens, or algae
SubkingdomTracheobiontaVascular plants—plants with a “circulatory system” for delivering water and nutrients
DivisionMagnoliophytaFlowering plants, also known as angiosperms
ClassMagnoliopsidaDicotyledons—plants with two initial seed leaves
SubclassAsteridaeA large class that encompasses asters
OrderAsteralesFlowering plants with a central disk flower and surrounding petals, like daisies
FamilyAsteraceaeThe aster family, which also includes daisies and sunflowers; from the Greek ἀστήρ, “star,” for the star-shaped flowers
GenusCentaureaFrom the Latin and a reference to the Centaur Chiron who was supposed to have discovered the medicinal uses of a plant in Greece that came to be called Centaury
SpeciesstoebeThe PlantzAfrica website says that the name of the genus Stoebe is from the Greek stoibe, “stuffing, padding or heap.” It was apparently used for packing wine jars and making brooms and bedding. Umberto Quattrocchi gives the following, also for the genus Stoebe: “Greek steibein, stibo “to tread firmly,” stoibe “thorny burnet, a species of Poterium,” Latin stoebe, es for a plant, called also pheos (Plinius).” From David Hollombe: “stoibe, name used by Dioscorides for Poterium spinosum, also meaning a cushion or pad”
ssp.micranthosSmall-flowered

About plant names...

Spotted knapweed, a native to eastern Europe, was introduced to North America in the early 1900s, as a contaminant in seeds for crops. It has since spread prolifically through much of the U.S. and Canada, where it competes with forage plants intended for livestock. It is considered an invasive species in many areas. Forage animals will eat it only as a last resort.

Identification: These ungainly plants average about 24" (60 cm) in height and reach up to 4' (1.2 m). The leaves at the base of the plant are somewhat pale, with oval-shaped leaflets growing alternately from the main portion of the leaf. Thin stems with many branches form a tangle in the upper part of the plant, with very narrow leaflets less than 1" (2.5 cm) in length. The flowers are a pink to purple (rarely white) in color, about ¾" (1.9 cm) in diameter, with each petal branching several times.

Spotted knapweed flowers bear a superficial resemblance to those of ragged robin: both disheveled-looking, both similar in hue. If you look closely, though, knapweeds are composite flowers (like other members of the large aster family)—they are composed of ray flowers and disc flowers. Ragged robin flowers have petals, but no central disc.

Centaurea stoebe (Spotted Knapweed)

Composite flowers, such as daisies, are typically composed of a central disc containing many small tubular disc flowers, surrounded by flat ray flowers. The ray flowers are often called petals, but each “petal” is actually a complete flower. Some composite flowers have only disc or ray flowers. “Composite” designates an aggregation of many small flowers that resembles a single flower, rather than two different types of flowers. The involucral bract is sometimes an important identifying feature—for example, this is where the spots are in spotted knapweed. Finally, the receptacle is where the parts of a flower head come together.

Spotted knapweed and ragged robin are compared below. See also Centaurea.

Online References:

Centaurea stoebe ssp. micranthos on the USDA Forest Service's Fire Effects Information Database

Centaurea stoebe ssp. micranthos on the Plant Conservation Alliance’s Alien Plant Working Group Least Wanted List

Centaurea stoebe ssp. micranthos on Forestry Images

Centaurea stoebe ssp. micranthos on Keir Morse's site, Keirosity.com

Centaurea stoebe ssp. micranthos at the USDA National Invasive Species Information Center

Centaurea stoebe ssp. micranthos on Invasive.org, Center for Invasive Species and Ecosystem Health (PDF)

Centaurea stoebe ssp. micranthos on SEINet—the Southwest Environmental Information Network

References:

Old, Richard, 1200 Weeds of North America DVD, XID Services, Inc., 2012

Uva, Richard H.; Neal, Joseph C.; DiTomaso, Joseph M., Weeds of the Northeast, Comstock Publishing Associates, 1997, p. 126

Newcomb, Lawrence, Morrison, Gordon (Illus.), Newcomb’s Wildflower Guide, Little, Brown and Company, 1977, p. 234

Peterson, Roger Tory, McKenny, Margaret, Peterson Field Guides: A Field Guide to Wildflowers of Northeastern and North Central North America, Houghton Mifflin, 1968, p. 92, 306

Centaurea stoebe (Spotted Knapweed)

7/31/2012 · Bemis Rd Conservation Area, Pepperell, MA
≈ 2½ × 2½" (6.7 × 6.5 cm) ID is uncertain

Centaurea stoebe (Spotted Knapweed)

7/24/2017 · WV

Centaurea stoebe (Spotted Knapweed)

8/4/2009 · Near Nashoba Hospital, Ayer, MA
≈ 16 × 12" (41 × 30 cm)

Centaurea stoebe (Spotted Knapweed)

7/24/2017 · WV

Centaurea stoebe (Spotted Knapweed)

7/24/2017 · WV

Centaurea stoebe ssp. micranthos description by Thomas H. Kent, last updated 24 Jul 2017.

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Centaurea stoebe (Spotted Knapweed)

That's a clearwing moth, possibly Hemaris thysbe, not a hummingbird! · 7/28/2013 · Andres Institute of Art, Big Bear Mountain, Brookline, NH
≈ 4 × 3" (10 × 8.4 cm)

Centaurea stoebe (Spotted Knapweed)

8/4/2009 · Near Nashoba Hospital, Ayer, MA
≈ 2 × 3" (5.4 × 7.5 cm)

Centaurea stoebe (Spotted Knapweed)

7/28/2013 · Andres Institute of Art, Big Bear Mountain, Brookline, NH
≈ 5 × 3½" (13 × 8.8 cm)

Centaurea stoebe (Spotted Knapweed)

7/21/2010 · Nashua River Rail Trail, Ayer, MA
≈ 5 × 8" (13 × 19 cm)

Centaurea stoebe (Spotted Knapweed)

7/28/2013 · Andres Institute of Art, Big Bear Mountain, Brookline, NH
≈ 5 × 3½" (13 × 8.8 cm)

Centaurea stoebe (Spotted Knapweed)

7/30/2012 · Tom and Susan’s, Pepperell, MA
≈ 3½ × 2½" (9.8 × 6.6 cm) ID is uncertain

Centaurea stoebe (Spotted Knapweed)

6/24/2017 · Tom and Susan’s, Pepperell, MA ID is uncertain

Centaurea stoebe (Spotted Knapweed)

7/31/2012 · Bemis Rd Conservation Area, Pepperell, MA
≈ 2½ × 2½" (6.5 × 6.6 cm) ID is uncertain

Centaurea stoebe (Spotted Knapweed)

8/6/2009 · Nashua River Rail Trail, Groton, MA
≈ 5 × 4" (13 × 10 cm)

Centaurea stoebe (Spotted Knapweed)

7/31/2012 · Bemis Rd Conservation Area, Pepperell, MA
≈ 2½ × 3½" (6.6 × 9.8 cm) ID is uncertain

Range:

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