Extrafloral nectaries

Caring for houseplants often leads to surprising discoveries. If you've ever spotted mysterious drops of sap on your plant's leaves and worried about diseases or pests, fear not. More often than not, it's just your plant doing what comes naturally. Those tiny sap drops may be a sign of something fascinating called extrafloral nectaries (EFNs).

EFNs are specialized nectar-producing glands strategically located on plant parts other than the flowers. Rather than indicating trouble, these small structures serve a vital purpose: they generate sweet nectar to attract beneficial insects that protect the plant.

Symptoms of pests or EFN?

When you encounter drops of sap on your plant's leaves, it's essential to rule out pest infestations. Pests can cause sap leakage from feeding punctures or leave behind sticky droplets of honeydew on and around your plant. Common culprits include spider mites, thrips, and honeydew-producing pests such as aphids, scale insects, and mealybugs.

Potential pests

1. Spider mites and thrips: These tiny pests puncture plant tissue, causing sap to leak. Fine webbing, stippled (flecked) leaves, dull grayish patches, and tiny black dots are common indications of spider mites or thrips.

2. Honeydew-producing pests (aphids, scale insects, mealybugs): These pests excrete a sugary waste substance called honeydew, which appears as sticky droplets on leaves and surrounding surfaces.

Distinguishing EFN from pests

1. Location: EFNs are found in predictable, consistent spots outside of the flowers. The undersides of leaves, petioles (leaf stems), and main stems are the most common locations. Some plants even have visible, raised bumps or glands where the nectar is released.

2. Appearance of sap drops: EFN nectar is typically clear, smooth, and odorless. A droplet is sometimes surrounded by a distinct border that can look yellow, black, purple, green, or red. In contrast, honeydew from pests is stickier, scatters randomly over a wider area, and often develops a dark coating of sooty mold over time.

Detecting and addressing issues

1. Regular inspection: Routinely inspect your plants for signs of pests. Check for webs, discolored patches, or visible bugs on the stems and undersides of leaves.

2. Wiping leaves: Gently wipe leaves with a damp cloth to clean away sticky residue and help the foliage breathe.

By understanding the key differences between extrafloral nectaries and pest infestations, you can better care for your plants and address genuine problems quickly.

Is EFN treatable?

In most cases, you don't need to treat or fix EFN at all, it's simply a natural defense mechanism to appreciate. However, environmental stress can cause plants to overproduce nectar or cause the surrounding spots to turn yellow, dry, or unusually pronounced. Here are a few stress factors you can actively address:

• Watering: Inconsistent watering, either too much or too little, stresses plants and can trigger increased nectar production.
  

  Solution: Maintain a consistent watering routine, following the instructions provided by Planta.
  

• Nutrients: Just like us, plants need balanced nutrition. Both a lack of nutrients and over-fertilizing cause stress.
  

  Solution: Ensure your plants receive the correct type and dose of fertilizer to prevent nutrient stress.
  

• Climate: Temperature extremes and improper humidity levels can stress plants and trigger EFN activity.
  

  Solution: Create a stable environment by monitoring and adjusting indoor temperature and humidity.
  

• Pests: Infestations cause physical stress that can prompt defensive nectar release.
  

  Solution: Manage pests promptly to keep your plants healthy and less likely to signal for outside help.

Do all plants produce EFN?

Many people haven't heard of extrafloral nectaries, but they have been documented in over 4,000 plant species across more than 90 plant families.

One of the most famous examples is cherry trees, which have visible glands directly on their leaf petioles. While botanists originally used these glands primarily to help identify species, they turned out to play an important ecological role.

The appearance of EFNs varies widely from plant to plant. Here are a few common houseplants known to produce them:

• Philodendron

• Goeppertia (Calathea)

• Hibiscus

• Passiflora

• Aglaonema

• Opuntia

• Rhipsalis

• Dioscorea