Are Tulips Heliotropic & Photonastic?

Heliotropic

• The term "heliotropism" refers to the ability of plant parts to track the path of the sun across the sky throughout the day. Tulips are heliotropic, which, according to York, Pennsylvania, florist Vincent Butera, means that even after being cut, the flowers will grow towards their source of light, sometimes by as much as several inches. Tulips and other heliotropic flowers can twist, move and bend throughout the day to position themselves in the best way to receive light.

Photonastic

• Tulips are plants that exhibit photonastic movements, which means they open and close in response to light intensity. This partially explains why most tulip species are closed during the night and open anew at dawn. Photonastic movements of are sometimes called "sleep movements," and they can be triggered by natural or artificial light.

Geotropic

• Butera also states that tulips are geotropic, which means that even after the flowers are cut, they will bend away from gravity. Geotropism is also called gravitropism, and this type of movement is the plant's response to the earth's gravitational pull. As an example of this, Butera notes that cut tulips arranged horizontally will bend upward, away from gravity's pull, and this is referred to as "negative geotropism."

Phototropic

• Tulips are phototropic, which means the direction they grow in is based on their position to a light source. Craig W. Whippo of Indiana University's Department of Biology states that phototropism is a plant's "complex biological response involving interactions of multiple photoreceptors, multiple hormones and multiple signaling pathways that together orchestrate the establishment of coordinated differential growth gradients." Simply put, the stem tips of tulips and other flowers that are phototropic will always grow towards their light stimulus.