Flowers of cocklebur (Xanthium strumarium) both ...

The image presents a dual-view comparison of cocklebur flowers, captured both in natural light and under ultraviolet (UV-A) blacklight illumination. The top photograph showcases the flowers in their natural state, while the bottom image reveals their fluorescence when exposed to UV-A radiation.

**Flowers in Natural Light:**

* **Location:** The flowers are situated on a stem, with some facing upwards and others downwards.
* **Coloration:** They display a pale greenish-yellow hue.
* **Structure:** Each flower consists of numerous small florets arranged in clusters at the end of a long stalk.

**Flowers under UV-A Blacklight:**

* **Illumination Source:** The flowers are illuminated by a 365 nm ultraviolet (UV-A) blacklight, which causes them to fluoresce.
* **Coloration:** Under UV-A light, the flowers exhibit a vibrant blue-green fluorescence.
* **Structure:** The florets appear more pronounced and distinct when illuminated by UV-A radiation.

**Comparison:**

* **Contrast:** The use of UV-A blacklight highlights the intricate details of the flowers' structure, particularly the florets, which are not visible in natural light.
* **Color Shift:** The coloration of the flowers changes significantly under UV-A illumination, shifting from pale greenish-yellow to vibrant blue-green.

**Background:**

* **Context:** The photographs were taken at Birch Creek Unit of Somerville Lake State Park in Texas on September 14, 2024.
* **Environment:** The setting provides a natural environment for the cocklebur flowers to thrive. – AI vision