Oddballs of the Plant World

Strange, stranger, strangest

Higher plants (and I will probably restrict myself to those that have seeds and are therefore referred to as Spermatophytes) are supposed to have roots, a stem, leaves, flowers and seeds, right? Fungi (mushrooms, toadstools and the like) used to be considered odd plants, but for quite a while now have been given their own “kingdom”, namely that of “Fungi”. Since they are not “autotroph” like plants and with the help of sunlight can turn water and CO2 into sugars and starch, but like animals require food in the form of organic matter, they have more in common with the latter than with the former. Also the fact that fungal cell walls are made of chitin (a carbohydrate typical of, for example, insects and kin, but not plants) and some fungi possess the enzyme collagenase, contain melanin, or are able to produce light, demonstrates that they share more features with animals than plants.

Let us start then with real plants that have no roots at all. The ones that immediately spring to mind are those of the genus Tillandsia. We had them in Jamaica on the electric wires next to our house. Not having roots they absorb nutrients and all they need (no, not from the wires), but from what is dissolved in the frequent rains of the tropics. They are what the botanist calls “epiphytes” (growing on other plants), a name that for Tillandsia had better be “epifilum”, but which is perfect for a plant like the mistletoe, which grows on trees, penetrates its host’s branches and obtains from the host plant nutrients and water. Since it also has green leaves and photosynthesizes like other green plants, it is a hemi-parasite and not a full parasite. Full parasites amongst higher plants do exist and the Australian and coral islands’ Cassytha starts as a green shoot, but becomes fully parasitic on a host and then loses its colour. The most spectacular parasitic plant with a flower up to a metre in diameter is Southeast Asia’s Rafflesia arnoldii. The flower, which is famous or better ’infamous’ for its awful putrid smell of rotting flesh is the only part of the plant visible, for there are no leaves, no stem, and the root is a modified organ to divert water and nutrients from the root of the host plant.

A very strange plant with a woody base and cones like a pine tree is also Welwitschia mirabilis. Confined to the Namibian desert, it can easily live on a minimum of moisture for a hundred years or more. But that is not the reason why I’d call it a plant oddball. No, the reason is that in its long life it only ever produces two leaves, which get torn and shredded by the wind and sand, but just keep growing. The tiniest flowering plants are the Lemna minor duckweeds and they lack a stem altogether, although they do have short and sticky roots that help the plant to get spread by water fowl and other temporary water visitors. I once got some of these tiny plants on the surface of my aquarium water to produce their tiny flowers, but usually they multiply by budding and no seeds. Seeds are also totally absent in the cultivated banana; in fact all seedless plants are actually oddballs.

To produce seeds plants need flowers and in the angiosperms (= the “flowering plants”) flowers are usually brightly coloured and symmetric. The oddballs are some plants of the genus Pedicularis, (known as “lousewort”), a root parasite, in which some species possess nectar lacking, highly asymmetric flowers. Which insects pollinate them (or whether it’s the wind) still needs to be studied. Pollination, in other words fertilization in seed plants, always occurs in the ovule at the base of the carpel by the pollen. The pollen can be regarded as a tiny, tiny plant, which is called a gametophyte and when it lands on the female structure of a flower, the pollen sends out a tube through which the tailless sperm can reach the ovule, i.e. the egg cell of the female gametophyte. Sounds complicated? Well, not for the plants, but what is odd is that only two groups of seed plant, namely the ancient gingko trees and the so-called cycads, (also known as ‘palmfern’ although they are neither palm nor fern) possess motile sperm with a tail like the spermatozoans one knows from most animals (not all have tailed sperm but that’ll be another essay). Someone might now wonder where that leaves the odd carnivorous and insectivorous flowering plants. Well, they too have their own separate essay.

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2018.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.

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