In the name of plants

Ricinus communis L. (castor oil plant) is a perennial shrub with big, palmately leaves. It is widely distributed throughout warm regions of the world, as it has been long time cultivated. But… What means “ricinus“?

Ricinus is the latin name of ticks, and the plant is so named because of its remarkable similarity with certain ticks:

Ricinus (seeds & ticks)

Arbutus unedo L. (the strawberry tree or Apple of Cain) is another Mediterranean and Western Europe shrub or tree. The Latin word arbor means “tree”, while unedo is formed by the Latin verb edo (to eat) and the numeral unus (one). So, as Andrés Laguna* explained, it means “eat only one”, regarding that its fruits, when mature, have a percentage of alcohol.

Arbutus unedo L.

However, we´re not interested in plants, but the names. As you can see in the examples, the scientific names are written in Latin. It is because the scientific name is not a random choice. Moreover, this is one of the many rules stablished by the International Code of Botanical Nomenclature (ICBN).

What is the ICBN?

Carl Linnaeus in Tulsa, OK (US)

Time ago (and even today), plants were named different depending on the language. This resulted in a complex situation in which a species had different common names, or the same name was given to different species. A paradigmatic case of this situation occurs with the Holm oak (Quercus ilex L.), a Mediterranean tree which has at least 8 different names in Western Europe: Holm oak, chêne vert, eiche, encina, alzina, artea, enciño, azinheira…

Common names are frequently related to characters, uses or properties of  the plants. Often it was different depending on the place, and this caused a big mess. Therefore, it seemed necessary to find a way to name the organisms undoubtedly: each organism must have a unique name.

Different systems were developed to solve this situation (you can read it in Wikipedia). One of these systems, the Linnaean system, was largely accepted (and adopted). Nowadays, Linnaean system is the mainstay of Taxonomy.

Taxonomy is the (ordered and hierarchical) classification of organisms (in this case, plants) according to a regular system. The names are given in base to the binomial nomenclature (popularized by Linné), and should be accepted by the ICBN.

ICBN (Vienna, 2006)

The ICBN contains a number of principles, rules and recommendations that must be followed to name species (and higher groups). These are the six principles (six very important principles!):

1. Botanical nomenclature is independent of zoological and bacteriological nomenclature. The Code applies equally to names of taxonomic groups treated as plants whether or not these groups were originally so treated.
2. The application of names of taxonomic groups is determined by means of nomenclatural types.
3. The nomenclature of a taxonomic group is based upon priority of publication.
4. Each taxonomic group with a particular circumscription, position, and rank can bear only one correct name, the earliest that is in accordance with the Rules, except in specified cases.
5. Scientific names of taxonomic groups are treated as Latin regardless of their derivation.
6. The Rules of nomenclature are retroactive unless expressly limited.

In addition to the principles, the Code provides a number of rules and recommendations, mainly about publishing names and about what makes a valid name.

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Addenda.

The most important things of the binomial nomenclature:

• The initial letter of the genus name is ALWAYS capitalized (i.e., Fagus L., Quercus L., Euphorbia L.).
• The initial letter of the species epithet is ALWAYS in lowe case (i.e., Fagus sylvatica L., Quercus robur L., Euphorbia pulcherrima Willd. ex Klotzsch). It´s a common mistake to capitalize it, so I hope that everyone who read this will be very careful…
• The WHOLE name is italicized (or at least, wrote different from rest of text).**

Notes:

* Andrés Laguna (1499-1549) was a Spanish pharmacologyst and botanist of the Rennaissance. His most relevant work is the translation (with additions) of Dioscoride´s De Materia Medica, a big work with descriptions of more than 600 medicinal plants (the precursor of modern pharmacopoeia).

** WordPress doesn´t allow me to do that with the images captions (growl…)

On the concept of plant (I)

When imaging a plant, we are probably thinking of a shrub, a herb, a beautiful flower or a large tree, with a big stem and many branches full of green leaves. Something like above.

People often talk about plants but, what do we understand as “plant”?

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For most people, the common concept of plant meets the following requirements:

• A life form
• Green
• Not moving

Well, I agree that a plant is a living being, an organism (maybe sometime we will talk about what “life” means). But, what about the other concepts? Through these aparently easy concepts, I´ll try to show what is (and what is not) a plant.

Are all plants green?

To be green, generally, means to do photosynthesis (i.e., being able to transform light energy into chemical energy. This chemical energy will be used to synthesize organic molecules). We think in plants as autotrophic multicellular phototrophs (which gain carbon molecules by doing photosynthesis). So, when imagine a plant, we think that they all are organisms able to do photosynthesis.

Rafflesia sp.

However, almost 3.000 species of vascular plants are known to be non-photosynthetic parasites (holoparasites). Specially significant is the parasitic biotype of some species of Rafflesia genus (Rafflesiaceae), native from Southeastern Asia (shown below). These plants don´t have leaves, stems or true roots, but only a large five petals flower (more than one meter in diameter, 10 kg weight in R. arnoldii R. Br.). The 15 species of Rafflesia are endoparasites of genus Tetrastigma (Vitaceae).

Then, are they plants? Sure they are. Holoparasitic plants have evolved independently in different lineages with mostly photosynthetic representatives (Santalales, Malpighiales, Saxifragales, Zygophyllales, etc.). So non-photosynthetic habit is currently interpreted as a secondary loss of photosynthetic capacity (though the photosynthetic relatives of them are mostly unknown).

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The kingdom Plantae includes (in addition to Embriophyta), green algae, red algae and glaucophytes. In fact, some of these groups are not mostly green.

So, the question is: plants are not always green but, everything green is a plant? Ok, that is not an easy question, but we will talk about that another time (will be continued…)

Are you sure that plants do not move?

Dionaea muscipula (Venus flytrap)

No? Then, what do you think about this poor fly? The video shows a Dionaea muscipula J. Ellis (Droseraceae) trapping its “nitrogen source”. As other insectivorous plants, D. muscipula lives in nitrogen and phospore-poor environments, such as swamps and wetlands. They use this and other techniques to obtain at least a part of its essential nutrients (not energy, just nutrients).

In the case of D. muscipula, the apical portion of its leaves is modified in two lobes. Each one of these lobes has some sensitive hairs in its inner face, and the tramp closes if the insect touches two of them in a range below 20´ (this has been interpreted as a security system to no trapping some “non-interesting” thing). Literally, this is a movement. A nastic movement.

A nastic movement is produced by an external stimulus, and is based in growing processes or changes in turgor in specific parts of the plant. The stimulus triggers the movement, but it doesn´t direct the orientation of the response.

Capture movements are not the only movements of plants, there are different movements in response to different stimuli. Of course, not every movements are present in every plants. Moreover, not every plants are able to move… but some yes.

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Another curious situation occurs in steppe and uncultivated lands (frequently hit by wind). Some plants, known as tumbleweeds, have adapted their dispersal mechanisms to these adverse environments. These plants, usually herbs, inhabit sandy areas all around the world, and their movement can be interpreted as a special anemocory: when the plant is fructified, the wind grubs up it from the soil. Because of this, seeds are released and dispersed.

Tumbleweeds are famous for starring in the Westerns (these actors are usually adscribed to the family Amaranthaceae).

Therefore the movements of plants exist, although they are not as conscious as those of animals.

Therefore, what is a plant?

In this first post we discussed about two typical ”plant characters”: photosynthesis and movement. However, there are many other characters that have traditionally been used to define the concept of plant.

Traditional Botany has studied different groups distantly related (fungi, algae and some others). The only common aspect between these groups was that they didn´t “eat” like animals do. That is why fungi, algae and land plants have traditionally been considered plants. Nowadays, it has been partially solved:

• Fungi are not considered plants because their cell walls contain chitin, unlike the true plants, which contain cellulose. Moreover, it has been probed that fungi are more closely related to animals than plants.
• Cyanobacteria were excluded in a new order, Monera. This order, not in use, is now considered in two new kingdoms: Archaea and Bacteria (including Cyanobacteria).

Excluding fungi and cyanobacteria led to a redefinition of Plant Kingdom, but did not end the discussion. In the next post, I will expose (as brief and clear as possible) the different points of view in such an important question.

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References:

• Baldauf, S.L. & J.D. Palmer (1993). Animals and fungi are each other´s closest relatives: congruent evidence from multiple proteins. PNAS, 90: 11558-11562.
• Barkman, T.J., S,-H. Lim, K.M. Salleh & J. Nais (2004). Mitochondrial DNA sequences reveal the photosynthetic relatives of Rafflesia, the world´s largest flower. PNAS, 101(3): 787-792.
• Engler, K. & K. Prantl (1887-1915). Die Natürlichen Pflanzenfamilien, 23 vols.
• Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 9, June 2008 [and more or less continuously updated since].
• Sitte, P., E.W. Weiler, J.W. Kadereit, A. Bresinsky & C. Körner (eds.) (2004). Strasburger: Tratado de Botánica. 35th ed. Ediciones Omega, Barcelona.