Plant Profile: Poinsettia (Euphorbia pulcherrima)

Native to Central America where it grows as an unattractive lanky shrub, the plants which are familiar today have been carefully cultivated using controlled lighting to produce colourful bract, usually red, but increasingly white, along with light and deep pink versions are available.

The plant was first introduced to the USA in 1825 by Joel Roberts Poinsett, an American dip. They were propagated by Robert Buist, a nurseryman who had migrated from Scotland to Pennsylvania, and made their public debut at a flower show in Philadelphia. The first poinsettias to arrive in Britain did so in bloom during November 1834. By the early 1900s had become a popular Christmas house plant.

The following story details the Mexican legend of how poinsettias became associated with Christmas:

Every Christmas Eve as everyone in the village gathered in the church for the Mass, every family would bring a gift for the Christ Child. Pepita. a young girl from in a small village in Mexico, had nothing to bring - her family was very poor. Her cousin Pedro attempted to console her. He told her, 'I am certain that even the most humble gift, given with love, will be acceptable in God's eyes!

Pepita was determined to bring something, so she found some flowering weeds along the side of the road. She made them into a bouquet, but she was embarrassed at the thought of bringing a bunch of weeds to lay before the manger. But it was the only gift that she had to offer.

The church was almost full by the time she arrived, and Pepita held the bouquet close to her side hoping that the others would not notice it. She hesitated before walking down the aisle, but she remembered the words of her cousin. She prayed, 'Oh God, this may not be the grandest of gifts, but may it be the gift given with the most love!'

Her spirits began to lift and she walked down the aisle holding the bouquet proudly in front of her. By the time she got to the front of the church her eyes were brimming with tears of love as she knelt and laid her bouquet in front of the nativity scene.

Suddenly, the bouquet of weeds burst into blossoms of brilliant red. And everyone there was certain that they had seen a Christmas miracle. From that day on the bright red flowers were known as the Flores de Noche Buena, or Flowers of the Holy Night. However, you know them as poinsettias.

Of course, we know that the brilliant red of the poinsettia do not relate to the actual flowers, which are non-descript and diminutive yellow-green. It is the bracts that surround the flowers that provide the attention-grabbing, lavish red, white or pinks. These colourful bracts do take the place of petals and are said to attract pollinators. Importantly, poinsettias are not annuals, but perennials that can be cared for between Christmas-time display: After Christmas, feed your poinsettia monthly with a high-potash liquid fertilizer, such as tomato feed, to promote healthy growth and flowering.

• In spring (around April or May), prune your poinsettia back to about 10 cm (4 inches) above the soil and repot it in a larger container with fresh potting mix. This will encourage new growth and branching.
• In summer (when the night temperature is above 10°C or 50°F), you can move your poinsettia outdoors in a shady location. Gradually acclimate it to more sun exposure until it can tolerate full sun. Continue watering and fertilizing as usual.
• In late summer (around July or August), pinch back the tips of each stem by about 2.5 cm (1 inch) to make the plant bushier and more compact.
• In autumn (from October to December), to make your poinsettia bloom again, you need to mimic short day length by placing it in a dark place (such as a closet or a cardboard box) for 12 hours every night. During the day, bring it back to a sunny spot and water and feed as usual. (Care instructions via Bing Chat Mode (OpenAI, 2023). ChatGPT (Dec 20 version) [Chat conversation]).

Plant Stems (Internal)

Personal notes for RHS Level 2 Certificate in the Principles of Plant Growth and Development

Unit 1: Plant Science 1: Internal Plant Structures: AO1 - AO2

The diagram illustrates a simplified stem followed by a close-up of the different layers.

Working from outer to inner tissues we begin with the epidermis, a protective, single layer, which produces an outer wax layer of cuticle call cutin, which is waterproof. Punctuating the epidermis layer are stomata pores, allowing gases to pass through the otherwise impermeable layer.

Underneath the epidermis is the cortex, largely constructed of unspecialised parenchyma tissue. These thin-walled cells are held in an approximately spherical shape by osmotic pressure, with many air spaces between them. This mass of cells also combines to assist with maintaining the plant shape, in addition to other functions, such as containing chlorophyll and releasing energy via respiration for use by surrounding tissues. In some plants, they can act as food stores, as in potato tubers.

Phloem and Xylem are the two vascular bundles within plant stems:
Phloem, containing long, tube-like cells, is responsible for transporting organic nutrients (such as sugars) from the leaves to other areas of the plant.

Xylem, containing long, wide, and open-ended cells with thick lignified walls, is the dead, permanent tissue located at the centre of the vascular bundle. It transports water and dissolved minerals from the roots to other plant parts.

In dicotyledons resides the vascular cambium, a lateral meristem which contains actively dividing cells that produce more phloem and xylem tissue. This increases the girth of the stem in woody plants and is known as secondary thickening. The bundles are arranged in a ring providing both strength and support.

Pith refers to the central zone of the stem, mainly made up of parenchyma cells. These can break down to leave a hollow stem.

There are two final cells to mention in this section, collenchyma and sclerenchyma:

Collenchyma provides extra mechanical and structural support, especially in regions of new growth. It helps young stems and leaves maintain their shape and withstand bending forces.

Sclerenchyma provides the main structural support to a plant. Unlike collenchyma, mature sclerenchyma cells are generally dead at maturity.