Versatile Aroids: from aquatic plants to climbers
Aroids thrive in very different settings, and have a wide range of types of growth.
When we look at Pistia stratiotes, which colonizes calm waters throughout the tropics and subtropics, who could believe that it belongs to the same family as the gigantic Philodendron goeldii, which climbs 20 metres above the ground to spread its tuft of leaves, some of them almost 2 metres long?
The Aroid family includes:
• aquatic plants, like Pistia and Cryptogyne,
• semi-aquatic plants, like Calla and Anubia,
• terrestrial plants, like Arisaema, Symplocarpus, Amorphyphallus and Anchomane,
• climbing plants, like Monstera and most Philodendron,
• epiphytic plants, like many Anthurium.
Most epiphytic Aroids are in the genus Anthurium. But there are also some lovely terrestrial Anthurium.
Anthurium is widely cultivated for cut flowers, in fact. It is easily recognizable by its large bright red spathe.
Epiphytic Anthurium can spend their whole life cycle on one host plant. They flower, produce fruit and germinate on a single plant. They produce adventitious roots covered in velum, as do orchids. In the wild, most of the Anthurium species cultivated at the Botanical Garden would be epiphytes, happily lodged in the treetops.
Monstera: a unique climber
Monstera has a very unusual growth habit.
When a seed germinates on the ground, the young seedling, rather than seeking the sun as one might expect, flees it and looks for darkness.
As the young plant grows, it creeps toward the shadowy base of a tree trunk. Once it attaches itself to the tree, the Monstera climbs to a height of several metres, regularly producing leaves, until it finds enough light to be able to start its reproductive phase.
Once mature, Monstera regularly produces enormous leaves nearly a metre across, on a thick rhizome attached to the tree. The axes it produces are very short, so that the plant always remains at the same height.
Colourful inflorescences periodically appear at the leaf axils, depending on how fast the plant is growing. Once it reaches the appropriate height to start reproducing, it puts out adventitious roots that extend down to the ground. This means that the main stem attached to the soil can break without affecting the plant’s growth. Philodendron shares this growth habit.
The reproductive organ: little-known flowers
While Aroids are widely known for their ornamental foliage, the same cannot be said of their flowers, which are most often hidden beneath the leaves or simply never develop.
Flowering in Aroids is so unfamiliar that people sometimes assume that the inflorescence of a Diffenbachia, for instance, is an anomaly.
And yet, when examined under a microscope, an Aroid flower contains a hidden world of shapes and colours.
What some would typically call a “flower” is in fact an inflorescence composed of numerous individual flowers, as in Asteraceae, except that, instead of being borne on a flattened axis, Aroid flowers are clustered along a long central spike, or column, and surrounded by an often colourful bract, called a spathe. The flowers and spike form the spadix.
Depending on the genus, the spadix can hold from two to more than 2,000 flowers. The miniscule inflorescences of Lemna minor, a plant native to Quebec, contain only three flowers, whereas some of the Anthurium in the Garden’s collections have been known to have close to 2,500, according to the Garden’s botanists.
The spadix looks roughly like a cylinder covered with rhombuses. In fact, each rhombus represents one flower consisting of a pistil and 4 stamens, with 4 tepals forming its edges. The 4 stamens are hidden within the tepals.They are usually visible only during anthesis, when the yellow or white swollen pollen sacs contrast with the green or burgundy tepals.
Some species occasionally produce a tiny drop of a sticky substance on the tip of the stigma. This is a secretion from the pistil designed to attract insects.
Fruiting in Anthurium begins with the development of the pistil, the female reproductive organ; tiny bumps appear on the surface of the previous spadix. As they grow, the fruits acquire their globular shape and characteristic colouring. The fruits, which in the botanical sense are berries like blueberries, are generally white, orange or red. Since each flower can bear only one fruit, a spadix will have as many fruits as there are pollinated flowers. What one sees on Anthurium and other Aroids, during fructification, is not one fruit but dozens or even hundreds of fruits.
But don’t expect to see flowers like these on all Aroids. In fact, while fructification is consistent within the family, the structure of the flower can vary considerably.
The flower of the Anthurium genus, which includes nearly 900 species, as well as of the Monstera, Spathiphyllum, Pothos and Acorus genera, is typically bisexual and is characteristic of nearly half of all Aroid species.
The other half features unisexual flowers, which grow on plants in such genera as Aglaonema, Philodendron, Amorphophallus and Arisaema.
Most genera that have unisexual flowers have no perianth. In other words, the flower is naked, and the pistil and stamens are exposed. Also, the male flowers occupy the top half of the inflorescence (spadix) and the female flowers the lower half. Aside from their position on the spadix, the male and female flowers have specific shapes that make it quite easy to tell them apart. The female flowers are usually globular with a flattened stigma, while the male flowers form angular clusters on the surface of the spadix. Often, a number of differently shaped sterile male flowers, called staminodes, can be seen between the male and female sections, as in the Philodendron, Xanthosoma and Colocasia genera, for instance.
Based on articles written Denis Barabé in Quatre-Temps magazine.