Ageratum conyzoides is under family Asteraceae. This species shows capitulum which is a head inflorescence. As we can see through the picture, Ageratum conyzoides is composed of tubular flowers. The corolla shows tubular structure. The flower of Ageratum conyzoides is syngenesious, meaning that its anthers are fused. Stamens are epipetalous. Epipetalous stamens are stamens attached to the petals. It is actinomorphic showing more than single plane of symmetry. Also, when you see the second picture, we can see that Ageratum conyzoides has pappus, which is white, hair-like structure. Ageratum conyzoides shows dry, achene type fruit.

There are similar, but different type of flower in family Asteraceae. Some species have both tubular and ligulate flowers. Ligulate flowers have flat corollets. Argyranthemum sp. is an example. To avoid intra competition, these flowers bloom the peripheral flowers first, then bloom the inner flowers. If you cut a single tubular flower of Ageratum conyzoides, we can learn that it has inferior ovary, meaning that the attachment point of other floral parts is above the ovary. Ageratum conyzoides has economical uses, such as food and medicine. In Central Africa, it is used to treat pneumonia, but the most common use is to cure wounds and burns.

What is curious about this species is that why doesn't it have ligulate flowers? What is the advantage of flowers having only tubular flowers, but no ligulate flowers? If ligulate flowers have specific function that is important, how could Ageratum sp. supplement or compensate that function?

https://hort.purdue.edu/newcrop/proceedings1999/v4-469.html