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Thistle Identification Referee 2017 Southwest Region
Deborah Meyer & Robert Price California Department of Food & Agriculture
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Purpose Review morphological characters that are useful for identification of thistle and knapweed fruits. Review useful resources for making identifications. Review resources used to make decisions on classification into common and noxious weed seeds. Identify seeds from less than ideal photographs.
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Referee Structure 15 questions on fruit morphology
Participants were to answer 28 questions related to identification of thistle and knapweed fruits: 24 multiple choice 4 short answer Participants were provided an identification guide consisting of color photographs and descriptions of 42 species of common and noxious thistle and knapweed fruits (Meyer 2017). Some questions required participants to use other reference resources of their choosing. Identification guide and questions distributed by the AOSA/SCST Executive Office to all members via , and posted on the AOSA/SCST Referee Committee website. 15 questions on fruit morphology 6 questions on fruit identification 7 questions requiring use of additional resources
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Overall Scores (% Correct)
Responses received from 87 participants. (38 government, 49 non-government)
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Percentages of Correct Responses
Blue = Morphology Green = Resource Management Dark orange = Identification Light orange = Identification + Resource Management
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Structures in General 11. What is the name of this structure? Hilum
Point of fruit attachment Stigma Style base 100% responses correct 13. This structure is: Attractive to ants Helpful to fruit dispersal Persistent on all fruits of Centaurea solstitialis Attached to the base of the inferior ovary 91% responses correct 10. The outer layer of this structure is Seed coat Testa Pericarp Perianth 74% responses correct 90% responses correct 14. What is the name of this structure? Hilum Point of fruit attachment Stigma Style base Fairly good responses on structures in general except for the fruit wall of the achene. 97% responses correct 12. What is the name of this area of the fruit in Centaurea? Pappus ring Scar rim Elaiosome ring Apical rim
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Structures in General 1. In the Asteraceae, the pappus represents this floral structure: Modified stigma Modified corolla Modified calyx Modified perianth 98% responses correct 15. The margin of this apical rim can be described as: Crenulate Dentate Lanceolate Oblanceolate 99% responses correct 16. What is the structure indicated by the arrow? Apical rim Elaiosome Hilum Style base 94% responses correct
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Association of Structures with Taxon
3. Which of the following genera has a pappus comprised of plumose bristles? Centaurea Carduus Silybum Cirsium 86% responses correct 2. Which of the following species has an epappose fruit? Centaurea calcitrapa Cirsium vulgare Onopordum acaulon Cynara cardunculus 97% responses correct 4. Which of the following species has the largest fruit? Cirsium arvense Cirsium japonicum Cirsium undulatum Cirsium vulgare 100% responses correct 17. What species has an inner pappus whorl consisting of a single broad scale? Carthamus lanatus Centaurea benedicta Mantisalca salmantica Volutaria muricata 97% responses correct 5. Which of the following species has a pappus that hides the style base? Volutaria muricata Mantisalca salmantica Centaurea solstitialis Crupina vulgaris 95% responses correct Required reading and understanding all the associated descriptions to answer the question.
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Additional Resources Required
6. Which of the following species is classified as a noxious weed seed somewhere in the United States? Amberboa moschata Centaurea cineraria Centaurea cyanus Mantisalca salmantica 97% responses correct 100% of participants used the All States Noxious List to answer question. 8. To what region of the world is Mantisalca salmantica native? South Western United States Mediterranean Region Southern Africa Pacific Northwestern United States 74% responses correct Resources used by participants varied. 28. According to Vol. 3 of the AOSA Rules, which name listed below is the currently accepted scientific name for Russian knapweed? Acroptilon repens Centaurea repens Centaurea picris Rhaponticum repens 98% responses correct
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Identification of Photos
These 3 questions related to this photo. 23. Name the species of the object circled and labeled as 23 in this photo? Centaurea diffusa Centaurea jacea Centaurea melitensis Centaurea solstitialis 32% responses correct 24. In what state is the object circled and labeled as 24 classified as a noxious weed seed? Nebraska Nevada New Jersey New Mexico North Carolina North Dakota 89% responses correct Question 23 – need to compare the ‘hook’ at the point of attachment. Correct answer is C. solstitialis – the hook is only slight, not nearly as pronounced as in C. melitensis. Additional clue, the length of the pappus in relation to the fruit length and the narrow spread of the pappus (C. melitensis pappus is shorter and has wider spread). Question 24 required participant to correctly identify the item circled – Centaurea cyanus – before they could determine in which state the species is classified as noxious. Participants needed to be able to recognize Onopordum as the genus considered noxious in California. Note there is an additional Centaurea solstitialis in the photo, but the question asked participants to name one other genus in the Asteraceae; therefore, Centaurea doesn’t qualify. 25. Name one other genus in the Asteraceae shown in this photo that is considered a noxious weed seed in California. Answer: Onopordum 84% responses correct
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Identification of Photos
21. What species is the contaminant in this white clover sample? Centaurea diffusa Centaurea solstitialis Centaurea stoebe Centaurea virgata 100% responses correct 18. What species is this? Carthamus oxycantha Carthamus tinctorius Centaurea jacea Rhaponticum repens 95% responses correct 19. What species is this? Carthamus oxycantha Carthamus tinctorius Centaurea jacea Rhaponticum repens 91% responses correct 20. The species in question #19 is: Pappose Epappose 79% responses correct Picture of safflower is a bit dark and the fruit is a little discolored making identification more difficult. The photo of epappose fruit of Centaurea solstitialis in white clover was correctly identified by all participants. Participants were also asked to state one character that helped with the identification. Photo of Russian knapweed – answer choices were all examples with white colored fruits. Participants were also asked to state whether the fruits of Russian knapweed are epappose or pappose. This required participants to read the description for this species in which it is stated the fruit has a deciduous pappus; therefore, the fruits a pappose. An epappose fruit will never have a pappus, whereas a pappose fruit may retain the pappus (persistent) or the pappus may be deciduous, thus giving the appearance of an epappose fruit.
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Identification of Photos
Carduus acanthoides Identification of Photos 26. What species is represented by the specimen labeled A? Carduus acanthoides Carduus nutans Carduus pycnocephalus Cirsium arvense Cirsium undulatum 79% responses correct Carduus pycnocephalus Carduus nutans 27. What species is represented by the specimen labeled B? Carduus acanthoides Carduus nutans Carduus pycnocephalus Cirsium arvense Cirsium undulatum 26% responses correct Cirsium arvense Sort of fuzzy photo of Carduus pycnocephalus (A) and Carduus nutans (B). Participants were to choose the correct name from the five answers provided. #26 most commonly mis-identified as Carduus nutans (musk thistle)(15 responses), followed by Carduus acanthoides (spiny plumeless thistle) (5 responses), Cirsium arvense (Canada thistle)(2 responses), and Cirsium undulatum (wavyleaf thistle)(1 response). #27 most commonly mis-identified as Cirsium arvense (Canada thistle) (49 responses), followed by Carduus acanthoides (spiny plumeless thistle) (15 responses) and Carduus pycnocephalus (Italian spiny thistle) (1 response). Cirsium undulatum
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