Question

${120}^o$ phyllotaxy occurs in

• A. Distichous
• B. Tristichous
• C. Pentastichous
• D. Octastichous

Answer 1

Answer: (B)

Tristichous

Phyllotaxy is the arrangement of the leaves on the stem. It is of 3 types, namely opposite, spiral and whorled. The spiral phyllotaxy is further subdivided into distichous, tristichous, pentastichous, octastichous and so on. Distichous phyllotaxy is also called as 1/2 phyllotaxy. In this type, the third leaf falls above the first and the fourth leaf base falls above the second and so on. It is seen in grasses. Tristichous phyllotaxy is also called as 1/3 phyllotaxy. In this, the first, fourth, seventh leaf bases falls on the same plane; the second, fifth, eighth leaf bases on the same plane and third, sixth and nineth on the same plane one above the other. In this, divergence is 120${}^0$. Pentastichous phyllotaxy is also called as 2/5 phyllotaxy. It is seen in Hibiscus. In this, sixth leaf base lies above the first one after completing two circles. Similarly, the seventh leaf base lies above the second leaf base. In this, divergence is 144${}^0$. Octastichous phyllotaxy is also called as 3/8 phyllotaxy. In this, the nineth leaf base lies above the first, the tenth lies above the second and so on. It is seen in papaya. In this, divergence is 135${}^0$.

Thus, the correct answer is 'Tristichous.'