Floral Morphology of Vegetables

Flowers: Reproductive organ of plant (P.C. D. Basak)

There are no doubt, to a biologist flowering is the most important and fascinating part of morphology and embryology of a plant. Like every plant, vegetables are no exception. Before the flowering commences, its precursor activity already takes place within plant where it’s decided when and where the initiation of flowering will be occurred. Many hormonal and structural changes are initiated which lead to flower primordium development.

Each species possess unique habits of flowering. In vegetable crops, plant generally produces three type of flowers: staminate (Androecious), pistillate (Gynoecious) and hermaphrodite. A majority of Vegetable crops like solanaceous vegetables, leguminous vegetables, okra etc. produce hermaphrodite flowers while cucurbitaceous vegetables produces many sex forms.

Read More: Floral botanical behaviour in tabular form

A brief flowering biology of some important vegetables

Potato:

Flower type is Cymose. Inflorescence is simple or compound type. Potato shoots are sympodium in nature and each terminates with a flower. Flowers are actinomorphic and with hypogynous ovary. Flowers have 5 petals, 5 stamen and 5 calyx lobes. Ovary is bilocular, superior and syncarpous type. Fruit type is Berry and have axile placentation. Petal colours varies from white to blue, reddish purple, bluish purple. Anther colour varies from green to lemon yellow, orange-yellow or deep orange. Each plant bear 25-30 fruit and each fruit contains 250-300 number of seeds. 1 gm True Potato Seed contains 1500-1750 number of seeds. Flowering in potato is promoted by high light intensity, long day length and medium temperature. Longer photoperiod of 16 hr and 20 ⁰C night temperature promotes flowering and reduces flower bud abortion. There are some genotypes (contrary to common genotypes) which fails to flower in long day and cool temperature condition. To overcome this problem various methods like, planting on bricks (Generally tubers are planted above the soil on bricks and covered with sand. After root was grown to soil the sand was washed), removal of tubers (to divert the sink of assimilates), Gibberellin spraying are generally suggested.

ReadMore: True Potato Seed

Potato flower and its different parts

Tomato:

Flowers borne in forked raceme cyme. They are generally 4-8 in number in a compound inflorescence. Flowers are pendent, hypogynous and perfect. Corolla is yellow to pale yellow in colour, and 6 in number. Both stamens and carpels are of 6 in numbers. Positional sterility is also observed where style protrudes with a flattened stigma through the androecium. The anther protective cone surrounds the stigma and ensures self-pollination. Stigma becomes receptive one day prior to anthesis. During that time corolla changes colour from light to dark yellow. Anther dehiscence occurs 1-2 days prior anthesis. Optimum temperature for pollination is 21⁰C. Honey bees and Bumble-bees are chief pollinator. Seed vernalization temperature is 5⁰C. Low temperature treatment induces flowering.  It’s been observed that if tomato seedlings are exposed to 14⁰C after cotyledon expansion produces greater number of flower per inflorescence. This treatment is very useful for early yield objective.

Tomato flower with pollinator

Chilli & Sweet Pepper:

Flowers borne in single or in cluster. Corolla rotate campanulate, deeply parted in 5-6. Stamens are 5-6 in number. Longitudinal anther dehiscence occurs. Ovary is 2-celed. Anther dehiscence takes place sometime after anthesis. Normally flowers remain open for 2-3 days. Maximum receptivity remains between 24 hours prior to anthesis to 6hr after anthesis. Cloudy and cold weather delays the anthesis. Chief pollinators are Bees, Thrips and Ants. About 16% natural cross pollination occurs. Fruit setting percentage is 40-50%. In sweet pepper anther dehiscence takes place 30 minutes after anthesis and pick receptivity remains from the day of anthesis to 2 days after anthesis.

Chilli flower-purple (P.C. D. Basak)

Chilli flower-white (P.C. D. Basak)

Ant as pollinator on chilli flower (P.C. D. Basak)

Eggplant/Binjal:

Inflorescence is often solitary but sometimes found in clusters also. Clusters are of 2-5 flowers. Flower drop is a major problem in cluster borne flowers (as high as 80%) compared to single flower (as low as 1%). Corolla is purple in colour. Although Self-pollination is a rule, heterostyly promotes cross pollination. 4 types of flowers are found in brinjal-

a.    Long styled with big sized ovary

b.    Medium styled with medium sized ovary

c.    Pseudo-short styled with rudimentary ovary

d.    True short styled with a very rudimentary ovary.

Among these only long-styled and medium-styled flowers set fruit naturally (70-86%) may be due to the positional and morphological advantage. Chances of Cross-pollination is more in Long-styled flowers. Temperature of 20-22⁰C with a 50-55% humidity possess highest pollen viability retains for 8-10 days. Short-styled flowers have low fruit-set may be due to poor viability of pollen grains or due to lack of pollen-stigma interaction. Morning is the peak anthesis time with peak stigma receptivity at the time of anthesis.

Brinjal flower and heterostyly

Cole crops:

Flowers borne in raceme on the main stem and its axillary branches. Inflorescence is 1-2m long while pedicel attains 1.5-2.0cm length. Both flattened and erect sepals are found. Flowers have 4 sepals, 4 petals, 6 stamens (Tetradynamous). Petals are generally bright yellow in colour. Ovary is superior and bi-carpelled with a false septum. Ovule is campylotropous. Flowers are generally protogynous. Anthesis starts in afternoon and completed in following morning. Anther opens a few hour later to anthesis. The fruit is pod and of glabrous siliqua type. Pollinators are Bees.

Typical flowers and fruits of cole crop

Radish:

Flowers are typical terminal raceme like crucifers with 4 sepals, 4 petals and are clawed. Cross pollination is predominant due to self-incompatibility.  Considerable inbreeding depression on selfing. Anthesis time is morning, between 9.00 am to 10.00 am. Pollen fertility is maximum on the day of anthesis. Stigma receptivity starts during anthesis and remain receptive after 4 days of anthesis. Fruit type is siliqua.

Radish flower

Carrot:

Inflorescence type of carrot is a compound umbel. The King umbel a.k.a. Umbel of the First Order or Primary Umbel flowers first. The umbels terminating the branches known as secondary umbel. The third umbel is completed in same fashion. Formation of first, second and other order umbel is completed in 7-9 days. In umbel, peripheral umbellate flowers open first followed by the linear umbellate flowers. The flowers are perfect with small petals, usually white to yellowish in colour. The calyx is entire. Number of stamen is 5. Ovary is inferior and consist of 2 locules, each with a single ovule. On the upper surface swollen nectar discs are present which support the stigma and style. All wild and cultivated species of carrots are andromonoecious and protandrous. Geitonogamy (fertilization of flowers with pollen grains from same or genotypically similar plants) is found in carrot where separation of male and female phases are completed at the level of the flower and umbel but these two phases overlap at the level of whole plant. Xenogamy (fertilization from pollen grains genetypically different species) is also found in carrot. Insects visiting adjacent umbels leads to xenogamy. Fruit type is schizocarpic.

Compound Umbel of Carrot

King Umbel

Beet Root:

Inflorescence type is spike. Flowers are almost sessile. Borne in clusters of 3-4 at inflorescence bract axils and at secondary branches. Flowers are inconspicuous, without corolla, but with green calyx which gets thicker towards base as the fruit ripen. Number of stamen is 5 and number of stigma is 3. Ovary sunk in disc. Tri-carpellate ovary contains only one ovule per ovary. Aggregated fruits formed from the collusion of 2 or more fruits and held together by swollen perianth (Calyx) base and thus forming an irregular dry corky Seedball or so called seeds. True seed is kidney shaped, small and of 3mm long. 1gm of seedball contains 50 numbers of seed. Seed viability is of 5-6 years.

Flowers and seeds of Garden Beet

Turnip:

Inflorescence type is a terminal raceme on the main stem. Other structures are similar to cole crops.

Cucurbits:

Cucurbits are highly cross-pollinated and are entomophillous. Honey bee, bumble bees are main pollinators. Flowers borne in leaf axils are mainly solitary or in racemose clusters. Flowers are large, showy and unisexual. Fruits are essentially an inferior berry with many seeds (exception: Chow-Chow). Parietal placentation is rule. Cucurbits exhibit various sex forms.

ReadMore: Sex forms of Cucurbits

Flowers of some cucurbit

Legumes:

Flowers are solitary and axillary. Flower type is racemeose. Can bear upto 3 flowers per raceme. Bracts very small, calyx oblique. Calyx lobes are unequal. Corolla colour varies from white, pink to purple. Cleistogamous in nature due to presence of a morphological barrier, named as Keel. Keels are short and incurved. Styles are falcate, flattened and bearded on inner surface. Stigma is minute and terminal. Anthers are enclosed inside the Keel prevents cross pollination. Stamens are of 10 in number and is Diadelphous (9+1). Anther colour is yellow to white. Ovary is monocarpelled and unilocular. Ovary possess multiple ovules. Generally flowers per node varies from 1-2 while in some cultivars it varies from 3-4.

Pea flower structure

Onion:

Onion inflorescence is a simple umbel, unlike carrot. Each ubel consists of flower buds or florets ranges from 200-600 in number. A single spathe which splits into segments when young flower emerges. Ovary is superior and placed as perianth above the stamen and petal. Ovary is trilocular with a nectary base. The Floral Stem is hollow in nature. The number of seed stem vary from 1-20 or more. The umbel is aggregated with cymes of 5-10 flowers each cyme. Flowers are white to bluish white in colour. Perianth segments are 6 in number with whorles spreading, reflexed and ovate in nature. There are 6 stamens in 2 whorles and those anthers are of bilocular type. Anthesis occurs in definite sequences and occurs between 9 am to 5 pm. The inner whorl dehisces first. At this stage stigma has no receptivity until the style elongates upto 5 mm. This requires 1-2 days. Onion is highly cross pollinated due to the presence of protandrous flower. The whole plant may remain in bloom for more than 30 days. The umbel development attend 7 stage of development, viz. non-floral, very small floral, small floral, medium floral, above medium floral, big floral and very big floral.

Onion flower

Flower morphology

Okra:

Flowers borne solitary or axillary (4th to 8th leaf, depending on cultivars). The narrow bractioles fall before fruit attends maturity. Calyx splits longitudinally during anthesis. Petals are 5 in number, 5-7cm long and of yellow colour with crimson claw. Numerous stamens per flower are found and stamen colours are united at the base. Ovary is superior type. Stigma is 5-9 in number and with 5-9 lobes and is of deep red in colour. Fruit type is capsule which dehisces longitudinally when ripened. Seed is green to dark brown. Flowering pattern is distinguishable as it starts from the below part and ends upward direction. The stigma receptivity is in peak before one day of anthesis. Flowering lasts for 18-20 hour. Anthesis occurs in the morning and overlaps with anther dehiscence. Anther dehiscence is transverse in nature. Pollen fertility is maximum between one hour before to one hour after anthesis. Flower remains open for short time and subsequently wither at evening. Bud pollination becomes unsuccessful as stigma become receptive only during anthesis. Basically self-pollinated but due to showy bright coloured corolla often cross-pollination occurred by the insects.

Okra flower and its structure

Palak (Spinach Beet):

Inflorescence is racemose with bracts of cymose type. Flower borne terminally or in axils. Flowers are small, sessile, hermaphrodite and bracteates (leafy). Ovary is perigynous. Number of stamen is 5. Pollen grains are light weighted, small and abundant in nature, that’s why pollination is done through air, thus anaemophillous. Highly cross-pollinated. About 35 days required to come in full bloom stage. Anthesis starts at early morning and continues upto evening. Low humidity and high temperature favours anthesis. Anther dehiscence occurs during mid-day. Stigma becomes receptive 8hr before anthesis with a pick period at just after anthesis. It may last even after 10hr of anthesis. Fruit is a Seedball.

Spinach:

Hermaphrodite forms are absent in spinach. The stem elongates to produce flower stalk. Flowers borne in cluster and vary from 6-12 in numbers. Sex expression varies in spinach. There are four kind of flowers found in spinach. 
a. Extreme male: These are smaller in size and bloom earlier than others. 
b. Vegetative male: These are larger in size.
c. Female: Larger in size and remain vegetative for longer time. Female plants bloom later in the season and flower at the same time.
d. Monoecious plants: Predominantly staminate, predominantly pistillate or purely pistillate. Flowering commences early with pistillate flower but with some staminates in later part of the season or equally staminate or pistillate throughout the season. Optimum Female: Male ratio is 60:40. 

Amaranthus:

Flowers are Glomerule type with monoecious sex form. Borne in cymes with both staminate and pistillate flowers.Ovary is superior, syncapous and bi- or tri-carpelled. Ovule is camylotropus. In A. tricolor & A. blitum cymes are clustered in leaf axil. In A. dubius terminally clustered, often axillary with smooth inflorescence. In A. hypocondriacus, A. cruentus, A. caudatus flowers are clustered terminally as panicle. 

Amaranthus spike and seeds