The mite sheltering in this barbasco domatium is only as wide as a human hair!  Photo by: Rosemary Glos

Is anybody home?

Structures that plants make to house helpful arthropods are called domatia (duh-MAY-shuh). These domatia provide shelter for mites. In return, mites help the plant by eating plant pests and cleaning their leaves. Mite domatia can be tufts of hair, caves, or tiny pits. Thousands of plant species make domatia; cooperation between mites and plants is important for both mite and plant success.

Common Names: Barbasco, Lukala, Mata-fome
Scientific Name: Paullinia pinnata
Family: Sapindaceae (Soapwort Family)

How do air plants live without soil?

Air plants absorb water and nutrients using special valve-like hairs.

Plants that grow on other plants but are not parasites are called epiphytes (EP-uh-fights). Many epiphytes, like this air plant, produce few or no roots. Instead, they absorb water and nutrients using specialized hairs called trichomes (TRY-combs).

These trichomes act like valves, letting water in when it is plentiful and preventing water loss when conditions are dry. 

Common Name: Air Plant                    
Scientific Name: Tillandsia sp.                 
Family: Bromeliaceae (Pineapple Family)

Water-absorbing hairs on a Tillandsia leaf. Each hair is slightly smaller than a grain of sand.  Photo by: Rosemary Glos

Phytoliths (white) on a sugarcane leaf. Each phytolith is about 20 microns long, less than half the width of a human hair! .  Photo by: Rosemary Glos

Gritty defenses

Plants can protect themselves from herbivores by putting silica in their leaves.

Silica is a hard mineral that forms the basis for sand and glass. Many plants produce specialized leaf cells filled with silica, called phytoliths (FIGHT-oh-liths, literally “plant stones”). Grasses produce a particularly diverse range of phytoliths. When insects or mammals chew on grasses, phytoliths wear down their mouthparts and slow their digestion. This deters herbivores and protects the leaf. 

Common Name: Sugarcane                 
Scientific Name: Saccharum officinarum                
Family: Poaceae (Grass Family)

Who lives in these tiny caves?

These cavities, called pit domatia, provide homes for predatory mites. 

Predatory mites eat tiny herbivores that feed on leaves. By sheltering predatory mites in their domatia, coffee plants encourage them to stick around and eat plant pests.

Scientists have a lot of unanswered questions about mite-plant interactions. Recent research conducted here at UM has shown that pit domatia like those made by coffee are more likely to evolve in tropical habitats, while tuft domatia are more common in temperate habitats. The reason for this pattern is still unknown.

Common Name: Coffee          
Scientific Name: Coffea arabica                
Family: Rubiaceae (Coffee Family)

Domatia on the underside of a coffee leaf.  Photo by: Rosemary Glos

Stomata on a Moses-in-a-basket leaf. The stomata are green from the light-harvesting pigment chlorophyll, while the surrounding cells also contain a pink pigment (called rhoeonin).  Photo by: Rosemary Glos

How do plants breathe?

Tiny pores allow gases to flow in and out of plant tissues. 

Like us, plants need oxygen to keep their cells alive. Most plants also need carbon dioxide for photosynthesis, the process by which they use energy from the sun to make sugars (food!) from carbon dioxide and water.

Plants control the movement of these gases by opening and closing groups of specialized cells called stomata (stoh-MAH-tah).

Common Name: Moses-in-a-Basket          
Scientific Name: Tradescantia spathacea          
Family: Commelinaceae (Spiderwort Family)

Leaves of many colors

Patterned plants have optical tricks up their (s)leaves. 

These begonias have two ways to make the striking patterns on their leaves: pigment-based coloration and structural coloration. Pigment-based coloration is relatively simple: cells are filled with vibrant chemical compounds, forming patterns. Structural coloration is trickier! Instead of using pigments, the plant changes the shape and arrangement of certain cells, making them reflect light differently. As a result, those patches of cells can look white, colorful, or even iridescent.

Common Name: Begonia          
Scientific Name: Begonia ‘Little Brother Montgomery’                
Family: Begoniaceae (Begonia Family)

This begonia combines green and red pigments with structural coloration to make showy patterns. Photo by: Rosemary Glos

Oil glands on the surface of a Meyer lemon leaf. The image seems blurry because the leaves are also covered with a layer of protective, translucent wax. Photo by: Rosemary Glos

Where do lemons get their smell?

Citrus leaves and fruit release fragrant oils from special glands.  

Close your eyes and imagine smelling a glass of freshly squeezed lemonade. Yum! That refreshing aroma comes from oils made by tiny glands in the lemon rind. Similar glands are found in the leaves. Citrus oils belong to a chemical class called volatiles (VAH-luh-duhls). Volatile oils evaporate on exposure to air, releasing characteristic fragrances. In addition to making lemonade smell nice, these oils protect the plant by killing harmful bacteria and deterring herbivores. 

Common Name: Meyer Lemon           
Scientific Name: Citrus x Meyeri               
Family: Rutaceae (Citrus Family)

All-in-one sunscreen and raincoat

Plants coat themselves with an array of protective waxes.

Cuticle is the outermost protective layer on aboveground plant tissues. Wax crystals deposited on top of the cuticle are called epicuticular (ep-uh-kyoo-TICK-yuh-luhr) waxes.

Epicuticular wax can be seen as a whitish bloom on leaves, fruit, and other plant parts. Its primary role is to keep water in or out of plant tissue. It can also reflect damaging UV light, prevent microbial infection, and make surfaces slippery for climbing insects. 

Ribbons of epicuticular wax on the surface of a date palm leaf.  Photo by: Rosemary Glos

Stellate trichomes on the underside of a cork oak leaf. Photo by: Rosemary Glos

Why make fuzzy leaves?

Plant hairs, called trichomes (TRY-combs), perform many useful functions. 
The branched hairs on cork oak leaves are called stellate (STEL-ate) or “star-shaped” trichomes. A dense covering of stellate trichomes can reduce water loss and regulate temperature during the hot, dry summers of this plant’s Mediterranean home.

Trichomes come in many shapes and sizes, including flat, barbed, and spherical. 

Common Name: Cork Oak                 
Scientific Name: Quercus suber              
Family: Fagaceae (Beech Family)

Bodyguards with a sweet tooth

Nectar-secreting glands that attract protective insects are called extrafloral nectaries (EFNs).

You may know that plants make sugary nectar to attract pollinators to their flowers. But nectar isn't just a flower power! Many plants produce nectar on other organs to attract sugar-loving insects, often ants. These insects defend their nectar source against herbivores, serving as plant "bodyguards." EFNs have been found in almost 4,000 plant species, from nearly every above-ground plant part. Next time you see ants on a plant, take a closer look - they might be visiting EFNs!

Common Name: Urucorana, Sangra-d’agua             
Scientific Name: Croton urucorana              
Family: Euphorbiaceae (Spurge Family)

Ants visit an urucorana extrafloral nectary in the greenhouse here at Matthaei Botanical Gardens. Photo by: Rosemary Glos

Plants produce a wealth of chemical compounds: over 120 have been identified in Pelargonium trichomes alone! Photo by: Rosemary Glos

Fragrant defenses

Scented geranium leaves are covered in tiny balls of fragrant oil.

Plant hairs that release chemical compounds are called glandular trichomes. When touched, the glandular trichomes on geranium leaves pop like tiny water ballons, releasing lemon-scented oils that are antimicrobial and toxic to herbivores. If you like how geraniums smell, you are not alone! Humans have come to love many of the chemicals that plants produce to deter herbivores. Herbs, spices, and perfumes often owe their potency to these defensive compounds

Common Name: Lemon-Scented Geranium              
Scientific Name: Pelargonium ‘Mabel Grey’               
Family: Geraniaceae (Geranium Family)

Got salt? 

Plants adapted to salty soils are called halophytes (HAL-uh-fights). 

Have you ever poured too much salt on your food? If so, you know that it is possible for things to be too salty! For plants, salty soils can cause nutrient deficiencies, dehydration, and toxic ion buildup. However, halophytes protect their cells from salt by blocking, storing, or excreting it.

Fourwing saltbush transports extra salt to bladder cells on the leaf surface. Over time, the bladders mature and burst, releasing the salt and coating the leaves in prismatic crystals.

Common Name: Fourwing Saltbush   
Scientific Name: Atriplex canescens   
Family: Amaranthaceae (Amaranth Family) 

Intact (blue) and burst (green) salt bladders on the surface of a fourwing saltbush leaf. Photo by: Rosemary Glos

Barbed hairs on the underside of a stingbush leaf. Photo by: Rosemary Glos

When plants bite back

Scented geranium leaves are covered in tiny balls of fragrant oil.

This stingbush is covered in barbed hairs that pierce and snag potential herbivores. 

Since plants can’t run away, they have other ways to defend themselves. For the desert stingbush, this means a coating of elaborate hairs (trichomes) with formidable barbs.

Leaves under the Lens curator and UM PhD student Rosemary Glos is studying stingbush and its relatives. Her experiments have shown that the barbed hairs trap and kill munching caterpillars. Next, she is investigating how the stingbush enhances its defensive cababilities using chemicals in its leaves.

Common Name: Desert Stingbush               
Scientific Name: Eucnide urens             
Family: Loasaceae (Stickleaf Family)

Water from thin air

The clumps of moisture-harvesting spines on cacti are called areoles (AIR-ee-uhls). 

Water is scarce in the deserts that cacti call home. Instead of relying solely on rainwater, many cacti use areoles to capture water vapor from the air. Areoles consist of tiny spines called glochids (GLOH-kids) embedded in a mat of sponge-like hairs. When water vapor condenses at the tip of a spine, the recurved barbs direct the droplet toward the base, where it is rapidly absorbed by the hairs. From there, it can be used by the cactus or stored for later in the plant’s fleshy tissue.

Common Name: Prickly Pear, Nopal   
Scientific Name: Opuntia deamii 
Family: Cactaceae (Cactus Family)

Areoles on the surface of prickly pear pad. The pad is technically a stem, meaning that glochids and the larger spines present on some areoles are highly modified leaves. Photo by: Rosemary Glos

Curated by Rosemary Glos

Rosemary is a PhD student in the UM Department of Ecology and Evolutionary Biology. Working with Dr. Marjorie Weber, she studies how microscopic plant traits influence interactions between plants and insects. Her research focuses on a plant family from arid regions of North and South America called the Loasaceae. Members of this family are known for their elaborate barbed, stinging, and glandular hairs, which have earned them nicknames like “stickleaf,” “stingbush,” and “chili nettle.”

Rosemary studies how these complex hairs protect plants from the elements and help them defend against herbivores. Each hair is tiny, ranging from just 75 microns (about the width of a human hair!) up to a millimeter long. To capture them, Rosemary employed a scanning electron microscope, which uses a beam of electrons to reveal features at the micron scale.