Certified Professional Horticulturist (CPH) Practice Exam

What condition is often indicated by purplish leaves on a plant?

1. Nutrient deficiency, specifically phosphorus

2. Overwatering leading to root rot

3. Underwatering leading to drought stress

4. Pest infestation impacting foliage

The correct answer is: Nutrient deficiency, specifically phosphorus

Purplish leaves on a plant are often an indicator of a nutrient deficiency, particularly phosphorus. Phosphorus is an essential macronutrient that plays a key role in energy transfer and photosynthesis. When a plant is deficient in phosphorus, it can lead to abnormal coloration in the leaves, typically manifesting as a purplish hue. This is because the plant may be unable to form enough anthocyanins, which can cause leaves to take on a purple tint. In terms of the other options, while overwatering can lead to root rot, which affects the overall health of the plant, it typically doesn't result in purplish leaves. Instead, symptoms of root rot might include yellowing leaves, wilting, and overall decline in vigor. Underwatering can lead to drought stress, which usually causes leaves to become crisp and brown rather than turning purplish. Pest infestations can cause a range of leaf symptoms, such as spots, holes, or discoloration, but purplish leaves are not a common sign specifically associated with pests. Thus, the presence of purplish leaves is predominantly linked to phosphorus deficiency.