| Neutral | htop | On Apr 13, 2007, htop from San Antonio, TX (Zone 8b) wrote: Malta thistle, Maltese star-thistle, tocalote, cockspur thistle, yellow star-thistle, Napa thistle (Centaurea melitensis) is an introduced invasive winter annual plant. It is difficult to distinguish between Malta star-thistle and yellow star-thistle (Centaurea solstitialis) until they flower. Both have bright yellow thistle-like flowers with prominent spines emanating from the flower base in a star-like arrangement at the base of the flower head. The spines on yellow star-thistle flowers are ¾ to1 inch long, yellow, very stiff and pointed like a cactus spine. Malta star-thistle has tan spines that are not as stiff and shorter (3/8 inch). Malta star-thistle bracts below the heads have short often reddish or brownish spines; whereas, yellow star-thistle bracts have yellow spines. Yellow-star thistle blooms have discoid heads that are about one inch in diameter. Malta star-thistle blooms stand 1/2 to 5/8 inch tall. Malta-star thistle blooms May-December with yellow star-thistle blooming April-September.
The following facts have been taken from the Encycloweedia webpage, Noxious Weed List, developed by the California Department of Food and Agriculture. I have placed YST to designate yellow star-thistle and MST to designate Malta star-thistle in front of each statement which assists one with identifying these plants.
YST - "Corollas mostly 13-20 mm long. Involucre (phyllaries as a unit) ~ 12-18 mm long"
MST - "Corollas typically 10-12 mm long. Involucre ~ 8-15 mm long"
YST- "Central spine of main phyllaries 10-25 mm long, stout, yellowish to straw-colored throughout. Lateral spines typically 2-3 pairs at the base of the central spine"
MST- "Central spine of main phyllaries 5-12 mm long, slender, typically purple- to brown-tinged; lateral spines usually 3-4 pairs, the upper pair on the central spine near the center"
YST - "Taproots grow vigorously early in the season to soil depths of 1 m or more, giving plants access to deep soil moisture during the dry summer and early fall months"
MST - "Taproots do not penetrate the soil as deeply as those of yellow starthistle"
YST- "Produces 2 types of achenes, both glabrous, ~ 2-3 mm long, with broad bases. Outer ring of achenes dull dark brown, often speckled with tan, lack pappus bristles, often remain in heads. Inner achenes glossy, gray or tan to mottled cream-colored and tan, with slender white pappus bristles 2-5 mm long"
MST - "Achenes ~2-3 mm long, finely pubescent, grayish to +/- tan, usually with slightly darker stripes. Bases deeply notched, narrow, hook-like. Pappus bristles pale tan, 1-3 mm long" |
