Cruciferae

Tetracarpellary ovary in Raphanus as against the two carpels in other Cruciferae (Brassicaceae)

We were taught that the Cruciferae is bicarpellary with a replum separating the 2 placenta. 

But the fruits of Rat –tailed raddish (Mougri- Raphanus sativus var. caudatus) are found to contain , two (1D) or four placenta (1F &G) in two (1D) or three (1E 1H) chambered fruits. One with 4 placenta are found to produce 2 seeds arising from opposing placenta (1I). 

This data indicates that the gynoecium is composed of 2 or 4 carpels.

 In addition, there appeared purplish oval/orbicular bract like appendages (BLAs) merged within the fruit wall at the base, appearing as an oval bulging/projection of the fruit, which appeared sterile carpels. The number of the BLAs varied from 2 (Fig. 1A) to 3 (Fig.1B) or 4 (Fig. 1C) in different fruits and corresponded to the carpel number of gynoecium.

 In fruits having two BLAs, seen on the opposite sides, inner cavity is 2-chambered separated by a replum and there are 2 placenta (Fig. 1D). 

Seeds are attached alternatively on opposing placenta. 

In fruits having 3 BLAs, fruit is 3-chambered, 3 placenta and seeds are seen in the central chamber (Fig. 1E). 

The fruits possessing 4 BLAs there are 4 placenta seen alternating with the  BLAs at the base(fig. 1F,G.) , but the fruit is 3-chambered and seeds are seen in the central chamber (Fig. 1H). These appendages appeared exactly similar to the fruits in anatomy having pericarp, placenta like regions and a central cavity and can be considered as sterile carpels retained in fruits. 

It is quite possible that these BLAs are sterile carpels incorporated in fruits.

 If that is so, the flower of this plant can be said to be polycarpellary similar to the ancestors of Brassicaceae. 

More studies are needed to verify these suggestions and assess the relevance of these appendages.

The carpel number of the gynoecium of Brassicaceae is a controversial  subject [1]. The tet­racarpellary theory assumed that the gynoecium is com­posed of four carpels; two sterile (valve) and two fertile carpels (solid), and the septum is true carpellary tissue, formed by the inward extension and subsequent fusion of the two fertile carpels. This theory was suggested by Eames & Wilson[2], Dickson[3] and  Merxmüller & Leins [4]. The bicarpellary theory assumed that; the gynoecium is composed of two carpels only, this theory was supported by Arber[5], Spratt[6] , Eggers[7] and Zohary[8]. The bicarpellary theory was accepted by most botanists in spite of certain obvious difficulties in explaining the nature of the septum. A recent study on 25 species of Brassicaceae representing seven tribes also supports the bicarpellary theory[9].

The present study supports the tetracarpellary theory of Eames & Wilson[2], Dickson[3] and  Merxmüller & Leins The data obtained by morphological and anatomical study of the fruits of Raphanus sativus  var. caudatusis intriguing and create more questions than answers. The presence of 4 placenta and 2 replum having the middle chamber with 2 seed bearing placenta indicates that the ovary is basically tetracarpellary. The  tet­racarpellary theory suggested by Eames & Wilson[2] , Dickson[3], Merxmüller & Leins[4] where it is assumed that the gynoecium is com­posed of four carpels; two sterile (valve) and two fertile carpels (solid) gets maximum support in the figures  1F and 1G as well as from 1H & 1I. The fertile centre chamber containing 1 (Fig.1H) or 2 seeds (fig.1I) indicates that this chamber is formed by the fusion of 2 fertile carpels. The two sterile carpels are seen on either side of the central chamber.

The occurrence of ovary having 2 placenta separated by replum as well as 4 placenta (also separated by replum) suggests that Raphanus sativus  var. caudatus is a transitional species. Since this genus is considered highly primitive[9], it might be showing a primitive tetracarpellary ancestry of Theales in few members, as well as the advanced bicarpellary condition of many of the other members of Brassicaceae. 

Source

M. Daniel (2022),  Tetracarpellary ovary in Brassicaceae -a case study with young fruits of Raphanus sativus L. var. caudatus ALEF. (rat tail raddish)

WORLD JOURNAL OF PHARMACY AND PHARMACEUTICAL SCIENCES, Vol. 11, Issue 12, 1695-1702.

Mammen Daniel