Sonntag, 18. November 2012

Plants of the Day (November 18th, 2012) - Citrus x aurantium L. and Citrus limon L.

This time, I want to introduce you two different and very popular plants to you. Both are crops and use for many different purposes. This plants are Citrus x aurantium L. and the other one is Citrus x limon L., which are both members of the Rutaceae family. In German, the first species is known as “Orange” or “Apfelsine” and the second species as “Zitrone” oder “Limone”. In English, C. x aurantium is known as “Orange Tree” and C. x limon as “Lemon Tree”.

C. x aurantium - habitus

C. x auratium is a medium seized tree, which can reach a maximum height of 10 metres (32.8 feet). It has a uniform canopy, which is richly branched. The branches are covered with thin spines. However, these spines are blunt and not piercing. The leaves are arranged in the alternating leaf-pattern. The leaf-blade is inverted egg-shaped and has a strong, dark-green colour. All leaves have a long, dark petiole

C. x limon - habitus 

The lemon tree is smaller and reach average heights between 5 and 7 metres (16.4 to 22.9 feet), what depends on the sort. The branches are also covered with blunt thorns, but the leaves are more laceolate. Both species are evergreen tree

C. aurantium - young fruits & leaves

The inflorescences of both species are racemes with only a few flowers per raceme. The flowers of C. x aurantium consists of five, fused sepals and five white petals. The also white stamens form a tubular structure around the stylus. The yellow stigma is very thick and stands out from the stylus. Flowering time is between February and June in Europe and from April to May in China.

C. x limon - flower

The inflorescence and flowers of C. x limon look similar. However, the colour of petals is more dirty white. In addition, the flowers of the lemon tree exude a stricter, more putrid smell.

Pollinators are insects but Anemophily and self-polination is also possible. The last method is very useful in breeding. 

C. aurantium - ripe fruit 

Both species are easy to recognize by their distinctive fruits: the orange of C. x aurantium and the lemon of C. x limon. In both cases, the ripe fruit are berries, which consist of three layers: Endoocarp, Mesocarp and Exocarp.

  1. The endocarp is subdivided into a few chambers, which contains the seeds . These chambers (10 to 13 at the Orange and 8 to 10 at the Lemon) are drained by many, thin channels, which have a yellow-green to red colour and contain the fruit juice. 
  2. The mesocarp of both plants is a bright white layer, which encircles the whole inner fruit. Through its colour, the mescorarp is also called “Albedo”.
  1. The endocarp (Flavedo) is the thin, outer layer, which protects the fruit and is responsible for the attraction of potential distributors. It has a green colour first but become yellow (lemon) or orange (orange) later

The fruits of species from the Genus Citrus contain a large amount of Vitamin C and Citric Acid, which give the fruits their characteristic, sour taste.

C. x limon - young fruit

As the x in the name suggest, both species aren't natural plants but hybrids. C. x aurantium is a hybrid between Citrus reticulata Blanco (Mandarin orange) and Citrus maxima (Burm.) Merr. (Pomelo), while the Lemon is a hybrid between C. x aurantium and Citrus medica L. (Citron).

Both species were first bred in China and India in ancient times (but the true origin is unknown). Later, they were brought to South Europe and Arabia by the Moors. Portuguese merchants like Vasco da Gama (1469 - 1524) brought it to Portugal later. Today, both plants belongs to the most cultivated plants on earth (especially the orange).

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