Glossary

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Aerial root: A root that grows above ground from the stem. Climbing plants use them to hold on to trees or a moss pole, and some also take up water through them.
Air layering: Propagation on the mother plant: a shoot is cut slightly, wrapped in damp moss and plastic film, and only separated once roots have formed at the wound.
Alkaloids: Nitrogen-containing plant compounds that can have a strong effect on the body even in small amounts. Many plants use them to protect themselves from being eaten; examples are caffeine, nicotine and the lycorine of the amaryllis family.

Bract: A modified leaf at the flower cluster. In the peace lily and other arum family plants it is called a spathe: a showy, often coloured leaf that wraps around the spike of tiny flowers and looks like one large flower.
Bulblet: A small daughter bulb that grows at the side of a bulb's base. Once it has its own roots, it can be separated and potted up on its own.

Calcium oxalate: A salt of oxalic acid. Many plants, among them the arum family, store it in their cells as fine, needle-shaped crystals. When chewed, they prick the mouth and throat and irritate the mucous membranes.
CAM photosynthesis: A water-saving form of photosynthesis (crassulacean acid metabolism). The plant opens its stomata at night, stores the CO₂ it takes in as malic acid and processes it during the day with its pores closed. Typical of cacti and other succulents.
Caudex: A strongly thickened base of the stem or root in which a plant stores water. In the ponytail palm it is the bulbous stem base that looks a bit like an elephant's foot.
Cyathium: The flower cluster of the spurge family: a small green-yellow cup full of tiny flowers that looks like a single flower itself. In the poinsettia the cyathia sit in the middle of the coloured bracts – which are modified leaves, not petals.

Dioecious: Male and female flowers grow on separate plants. Fruits and seeds only form when a female plant is pollinated by a male one.
Dormancy: A break in which a plant grows little or not at all. Bulbs pull back their leaves and live on their reserves – many need this cool, dry phase to form new flowers.
Drainage: A draining layer in the pot (e.g. expanded clay, coarse gravel) plus a drainage hole, so that excess water can run off and the soil doesn't become waterlogged.

Epiphyte: A plant that grows on trees instead of in the ground, without tapping into the tree. It gets water and nutrients from rain, air and decaying leaves in the forks of branches.

Finger test: Push your finger two to three centimetres into the soil: if it feels dry, you can water. Simpler and more reliable than any watering schedule.
Frond: The name for the leaves of ferns (and palms). In ferns they unroll like a bishop's crook as they emerge and are usually divided into many leaflets.

Hemiepiphyte: A plant that germinates high up on a tree as an epiphyte and only later reaches the ground with long roots – like many tropical figs. A true epiphyte, by contrast, never touches the ground in its whole life.

Nyctinasty: The “sleep movement” of leaves in a day-night rhythm: plants such as calatheas fold their leaves upwards in the evening and open them again in the morning – which is why their relatives are called "prayer plants".

Offset: A young daughter plant that sprouts from the mother plant (often from the rootstock) and can be separated and potted up on its own.

Rhizome: An underground stem, usually growing horizontally (“rootstock”), that stores water and nutrients and sends up new shoots.
Runner: A thin, often long side shoot that grows out of the plant and, where it touches the ground, forms roots and a new daughter plant.

Saponins: Bitter plant compounds that foam in water. In larger amounts they irritate the mucous membranes and the gut – typical in pets: drooling, vomiting, diarrhoea.
Short-day plant: A plant that only sets flowers once the nights get long enough – that is, in autumn. Even a lamp in the evening can interrupt the long night and prevent flowering.
Spores: Tiny reproductive cells of ferns, mosses and fungi. Ferns form them in small clusters (sori) on the underside of the fronds – instead of flowers and seeds.
Spur: The stalk (peduncle) a hoya's flower cluster sits on. It stays on the plant after flowering, and new flowers can form on it again – so don't cut it off.
Succulent: A plant that stores water in thick, fleshy leaves, stems or roots and so survives long dry spells. Examples: cacti, aloe, snake plant.

Tubercles: Small, cone-shaped bumps on the body of some cacti. The spines sit on their tips.

variegated: Patterned in several colours: leaves with white, yellow or cream edges or patches, because less leaf green (chlorophyll) forms there.

Waterlogging: Water that is left standing in the pot or cachepot. The roots no longer get oxygen and start to rot – the most common cause of death in houseplants.
Winter rest: A cool, dry break in winter during which many cacti and succulents hardly grow. The plant keeps its leaves but needs very little water and no fertiliser.