Nomenclature

Species name:

Geranium purpureum   Vill.

Author(s):

Domínique Villars
   France, 1745-1814

Common name:

Little Robin
Lesser Herb Robert
Purple Herb Robert

Maltese name:

Ġeranju roża

Plant Family:

Geraniaceae   (Geranium Family)

Name Derivation:

Geranium = from the Greek geranos - "crane", referring to the slender beak-like fruit (Greek);

purpureum = Purple, should be referring to the deep purple flowers, but the young plants tend to have a reddish-purple colour too. (Latin).

Synonyms:

G. robertianum subsp. purpureum (main synonym) , G. lebelii, G. mediterraneum, G. minutiflorum, G. modestum, G. scopulicola, G. semiglabrum , G. villarsianum

Remarks:

Some taxonomical systems place this species under G. robertianum subsp. purpureum as the accepted taxon.

Plant Description

Life Cycle:

Annual or Biennial

Habitat:

Valleys, shady or humid places,

Sources in Malta:

Locally frequent. Examples include Wied Incita, Buskett, Mistra and Mgarr ix-Xini (Gozo)

Plant Height:

10-50 cm

Flowering Time:

Feb-May

Geranium purpureum is morphologically similar to Geranium robertianum and in fact, some taxonomists put it as a subspecies of the latter ( ie G. robertianum subsp. purpureum). The humid-loving plant is an annual or in some habitats biennial with an ascending growth-form in shady places and procumbent in more sunny ones.

The leaves are so well deeply cut that they give the impression of being a compound leaves with separate leaflets. Adult leaves usually have 5 distinct lobes while younger plants might produce only 3. Each leaflet-like lobe is further cut into 2 or sometimes 3 lobes (referred in this case as segments) which in turn, each segment is shallow-lobed. This repeated and somehow symmetrical lobing forms a beautiful general leaf pattern. The degree of pinnatisection (lobing) depends on the size and age of the leaf. Leaves measures 3-8cm wide and on a closer look to the segment lobes, one can note a small tip at their tip (in botany referred to as apiculate).

The actinomorphic flower is made up of 5 free sepals and 5 free bright purple petals. The green sepals are oval with a short bristle-like tip. During the bud phase, the sepals are found converging onto each other to form a closed calyx and at this stage, their long erect translucent bristles are more conspicuous than at the flowering one. The flowers of G. purpureum are smaller from G. robertianum, having petals 5-10mm and 10-14mm long respectively. The petal limb is also shorter by about 3mm and is found to be between 3-5mm long. The base of the petals narrows to what is known as a claw. This narrowing is less abrupt than in G. robertianum, and hence make the claws of G. purpureum slightly broader.

The male reproductive organs are 5 erect filiform stamens which produce yolk-yellow pollen and so differs from that of G. robertianum as the latter produce orange-amber pollen. The female reproductive part is rather unique as in other Geraniaceae members especially when it comes to seed dispersion.

The superior ovary initially consists of a carpel (more precisely a schizocarp) consisting of 5 joined mericarps. This species has a glabrous mericarp with about 4 strong transverse ridges near the apex and a network of finer ridges at the central and lower part. On maturity, the mericarp separate and later it becomes detached from the receptacle by a complex mechanism described below. Seeds are brown, about 1.5mm long, and have an oval shape.

On maturity a tapering columnar structure, referred to as a beak, grows to a variable length of few cms. The beak should not be mistaken as an enlarged ovary but it is actually an enlarged and specialized style. The mericarps are connected to the beak by a rigid, sheath-like structure referred to as the rostrum. In other words, the rostrum makes part of the outer wall of the beak, where one end is attached to the basal mericarp, and the other to the upper part of the beak. When mature, the shrinking rostrum breaks the mericarp in half and rolls it inwards towards the beak with a sudden mechanical movement. While it pulls violently the mericarp off from the receptacle, the single seed inside the broken mericarp eject out at a considerable distance away. What is left is a coiled rostrum with an empty, half broken mericarp.

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