Olearia adenocarpa facts for kids

The Olearia adenocarpa, also known as the small-leaved tree daisy, is a special shrub found only in New Zealand. It belongs to the Asteraceae plant family, which includes daisies. This bush can grow up to 1.5 meters (about 5 feet) tall and 1.2 meters (about 4 feet) wide. It's a bit smaller and more open than its cousin, the Olearia odorata. This plant can lose all its leaves in winter (deciduous) or just some of them (semi-deciduous).

What Does the Olearia adenocarpa Look Like?

This plant grows new branches from the ground often. This is because its main branches don't live very long, usually up to 12 years. The branches can be up to 30 millimeters (about 1.2 inches) thick.

Some branches lie along the ground with their ends curving up. Others grow straight up. It can also send out roots and shoots from its stems, which helps it spread.

The leaves of the Olearia adenocarpa are egg-shaped and grow in pairs. They are small, about 3 to 14 millimeters long and 2 to 4 millimeters wide. The top of the leaf can be light green, brownish-green, or grey-green. The underside is covered with soft, silvery-white hairs.

Flowers and Seeds

Clusters of pale white flowers with a yellow-green center start to bloom in January. When the flowers open, they release pollen from tiny parts called anthers. The seeds are dry and covered with fine hairs. These hairs are a key feature that helps scientists tell this plant apart from other similar species.

Where Does the Olearia adenocarpa Live?

Global Home

The Olearia adenocarpa is a rare plant. It is one of only eight rare Olearia species found around the world. In total, there are about 180 known Olearia species across Australia, New Guinea, and New Zealand.

New Zealand Home

This plant is found only in the Canterbury Plains on the South Island of New Zealand. There are only two main groups of these plants left. One group is near the lower Rakaia River, in an area called Great Island. The other is in the Waimakariri River floodplain, between Harwood and West Melton.

To help protect this rare plant, a special fenced area has been set up. This area is watched closely to help the Olearia adenocarpa grow and prevent it from becoming extinct.

Life Cycle and Reproduction

Scientists don't know a lot about the full life cycle of Olearia adenocarpa. This is because there are so few of these plants left.

When the plant is about 6 months old, its main stem starts to lie along the ground. By one year old, it usually has two or three main branches lying down and a few shorter upright branches. At two years old, it can have more than 12 branches that lie along the ground, each 3 to 12 centimeters long, plus many other new shoots.

Once the plant is three years old or more, it is considered mature. It will have more than 18 thin branches. However, these branches don't live very long. Scientists can tell this by looking at the plant's growth rings, which show that branches usually live no more than 20 years. You can often see old, dead branches scattered around the base of the plant.

How Grazing Affects Growth

How well the plant grows depends a lot on how much animals graze on it. Plants that are grazed a little bit grow new shoots regularly. But plants that are heavily grazed produce very few new shoots. This means that when older branches die, new ones don't grow to replace them. Over time, the plant can die from being eaten by animals like hares, rabbits, or sheep.

Flowering and Seed Dispersal

The flowering time, or phenology, of Olearia adenocarpa is also not fully known. This is because the species was only recently discovered, and there are so few plants.

Flower buds start to appear in mid-December, growing to about 0.1 centimeters. By late December, they are about 0.2 centimeters long. By mid-January, the buds are about 0.4 centimeters long. The flowers usually open around the end of January. This is when the first tiny flowers open, and the anthers release their pollen. These flowers often grow in clusters.

The flowering period finishes by the end of February. By then, all the pollen has been released, and the dry seeds are covered with fine hairs. Scientists think that seed dispersal might happen when flood waters from the river carry the seeds downstream. However, the hairs on the seeds also suggest that they might be carried by animals like sheep or rabbits.

Habitat and Adaptations

The Olearia adenocarpa does not have special parts on its roots that help it get nitrogen from the air. So, it grows best in soils that don't have much nitrogen. Instead, it uses phosphorus from the soil. The soils where this plant is found are quite fertile, meaning they have good nutrients, and their pH level is fairly neutral.

However, the Olearia adenocarpa lives on dried braided river beds. This means the environment can be very harsh. It can experience very dry, drought-like conditions with strong sun and little water. But it can also be completely covered by flood waters from the river. The plant has adapted to these tough conditions by growing low to the ground.

Threats and Conservation Efforts

The Waimakariri River area is where most Olearia adenocarpa plants are found. Sadly, up to 95% of these plants are eaten by animals. The main animals that eat this plant are hares, rabbits, and sheep.

This grazing has greatly changed how the Olearia adenocarpa grows. Plants that are grazed have older, thinner, and shorter branches compared to those that are not grazed. Since this plant species is very rare and has such a small population, heavily grazed plants cannot reproduce or grow well. Researchers believe that only Olearia adenocarpa plants that are not grazed can reproduce.

New Discoveries and Future Challenges

There are only about 650 individual Olearia adenocarpa plants left. For a long time, this plant was mistakenly identified as Olearia odorata or Olearia virgata. But thanks to new discoveries and better ways of studying plants, including using modern technology, Olearia adenocarpa was officially described and named in 2004. This suggests that it might be a natural hybrid, meaning it formed from two different species, which is common in the Olearia group in New Zealand.

It's unlikely that the population of Olearia adenocarpa will grow much in the future. This plant needs natural events like erosion or flooding to create new, open ground for its seeds to spread and grow. However, with more infrastructure being built to protect roads and water systems, these natural events are being prevented. This limits the chances for new Olearia adenocarpa plants to grow and spread.