Vexillary / Papilionaceous Corolla: Standard, Wings and Keel
Biology · Morphology of Flowering Plants · NEET
A papilionaceous (butterfly-shaped) corolla is the pea/bean flower type. It has 5 petals: one large posterior petal called the standard (also called vexillum), two lateral petals called wings, and two fused anterior petals forming the keel (carina). Memory hook: "So We Kick" = Standard, Wings, Keel, from top to bottom. The standard overlaps the wings, which overlap the keel, so this aestivation is named vexillary.
A pea corolla has 5 petals: one posterior standard (vexillum), two lateral wings (alae), and two fused anterior petals forming the boat-shaped keel (carina). The standard overlaps the wings, which overlap the keel, giving vexillary aestivation.
Your doubts, answered
What is the standard petal also called?
The standard petal is also called the vexillum. It is the single, largest, posterior (back) petal of a pea/bean flower. Because this large petal overlaps the others in the bud, the whole aestivation is named vexillary. NEET 2016 asked exactly this: standard = vexillum.
What is the difference between standard, wings and keel?
They are the three parts of a papilionaceous corolla by position. The standard (vexillum) is the one large posterior petal. The wings (alae) are the two lateral (side) petals. The keel (carina) is the two anterior (front) petals that are fused and boat-shaped, and they enclose the stamens and pistil. So it is 1 + 2 + 2 = 5 petals total.
Is the keel one petal or two?
The keel is made of two petals, but they are fused (joined) to look like the boat-shaped bottom of the flower. This is why the count is standard (1) + wings (2) + keel (2) = 5 petals. Students lose marks by counting the keel as one petal.
Why is this aestivation called vexillary?
Aestivation is how petals are arranged in the bud. In pea, the large standard (vexillum) overlaps the two wings, and the wings in turn overlap the two keel petals. Because the vexillum leads this overlapping order, NCERT names this special descending-imbricate type vexillary. It is a type of imbricate aestivation seen only in the pea sub-family (Papilionoideae).
Which plants show a papilionaceous corolla?
Members of family Fabaceae, sub-family Papilionoideae, such as pea (Pisum sativum), bean, gram, sesbania and Lupin. In NEET 2022, Pisum sativum was the answer for the plant showing vexillary aestivation and diadelphous stamens. These same flowers are also zygomorphic (bilaterally symmetrical).
⚠️ The NEET trap ✗ Standard petal is also called Corona or Pappus. ✓ Standard petal is also called Vexillum. 🧠 NTA mixes in corona (a perianth outgrowth) and pappus (modified calyx of Asteraceae) as traps. Only vexillum belongs to the pea flower. Match the term to the correct family: pappus = sunflower family, corona = Passiflora/Datura, vexillum = pea.
Real NEET questions
2016
The standard petal of papilionaceous corolla is also called:
A · Carina
B · Pappus
C · Vexillum ✓
D · Corona
Solution: In a papilionaceous (pea/bean) corolla the largest posterior petal is the standard, which is also called the vexillum (hence the aestivation is termed vexillary). The two lateral petals are wings (alae) and the two fused anterior petals form the keel (carina). Pappus (modified calyx of Asteraceae) and corona (a perianth outgrowth) are unrelated. Answer: Vexillum.
2023
In a pea flower, five petals are arranged with one posterior, two lateral and two anterior. These are named as ___, ___ and ___ respectively.
A · Keel, Standard and Carina
B · Standard, Wings and Keel ✓
C · Keel, Wings and Standard
D · Vexillum, Keel and Standard
Solution: Posterior petal = standard (vexillum), the two lateral petals = wings (alae), the two anterior petals = keel (carina). So posterior, lateral and anterior correspond to Standard, Wings and Keel. Answer: Standard, Wings and Keel.
2022
Which one of the following plants shows vexillary aestivation and diadelphous stamens?
A · Colchicum autumnale
B · Pisum sativum ✓
C · Allium cepa
D · Solanum nigrum
Solution: Vexillary (papilionaceous) aestivation, where the large standard overlaps the two wings which overlap the two keel petals, plus diadelphous stamens (9)+1, are diagnostic of the pea group (Fabaceae, Papilionoideae). Only Pisum sativum (pea) shows both. Colchicum and Allium are Liliaceae, Solanum is Solanaceae. Answer: Pisum sativum.
Solved Morphology of Flowering Plants NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Five petals: one standard, two wings and two keel petals (1 + 2 + 2 = 5).
What is the shape of the keel?
The keel (carina) is boat-shaped and formed by two fused anterior petals. It encloses and protects the stamens and the pistil.
Is papilionaceous corolla the same as vexillary aestivation?
They describe the same pea flower. Papilionaceous refers to the butterfly-shaped corolla; vexillary refers to how those petals overlap in the bud. Both are used for the Fabaceae (Papilionoideae) flower.
Is a papilionaceous flower zygomorphic or actinomorphic?
It is zygomorphic (bilaterally symmetrical). A pea flower can be cut into two equal halves in only one vertical plane, which is why NCERT lists pea as zygomorphic.
What are the wings also called?
The wings are also called alae. They are the two lateral petals lying between the standard and the keel.
