What does "Huayang" in ancient poetry usually mean?

Huayang: Catkin.

When poplars fall, cuckoos sing, catkins fall and cuckoos sing.

Poetry: "I heard that Wang Changling moved to Zuo Long to express this letter" Tang Dynasty: Li Bai.

After the easy autumn, cuckoo clock, I heard you pass five streams. I entrust my sad thoughts to the moon, hoping to accompany you to the west of Yelang.

I heard that you will pass by Wuxi, a place where flowers fall and Zigui sing. I put my sad thoughts on the bright moon, hoping that it can always accompany you to Yelangxi with the wind.

Extended data background: I heard that Wang Changling moved to Longbiao Kiln to the left, which was written in 753 AD (Tianbao 12th year of Emperor Xuanzong of Tang Dynasty). At that time, Wang Changling was demoted from Jiangningcheng to a captain in Longbiao County (now Qianyang County, Hunan Province), and Li Bai wrote this poem after hearing that his friend was demoted to Yangzhou.

Appreciation: The poet expresses like-minded friendship in the way of love between men and women through rich imagination, endowing the abstract "sad heart" with the property of things, and it will go to Yelangxi month by month with the wind. Yue Ming, who was originally ignorant and heartless, turned into a bosom friend, full of sympathy. She was able and willing to accept her request, and brought her nostalgia and sympathy to the distant west of Yelang and gave it to the unfortunate immigrant.