Last year, this plant showed up in my Zone 5 garden. It's a very symmetrical plant with many 2" vivid yellow blossoms with a brown eye and 13 petals. The leaves are deep green, whorled and ligulate. They're rough front and back. It stands about 3 to 4' tall, enjoys full sun, average soil, and is watered every other day in a drought. On the whole, pests and diseases pass it by. I loved it for its symmetry, but now that it is blooming (started 2nd week of October), its branches have relaxed and moved away from its center. I had thought it had one stem and many small twigs but that's obviously not right. One garden club and our local horticultural office are searching for its identity but so far it remains unknown. Sunflower, rudbeckia and aster have been suggested, but without anyone able to locate a matching picture. I'm leaning toward a mum ID but have no proof. I hate just calling out, "Hey, you!" to get its attention, so if you know what it is, please let me know! Thanks.
I finally got in touch with a grower who osupplied a nursery where I had seen it while on vacation. She identified it as what you said, Helianthus angustifolius, but that particular one was 'golden lace'. Thank you for your suggestion. It provided enough information to be able to identify it enough.
