Goat Weed (Ageratum sp.), Sida Acuta, And Crotalaria Retusa As Biological Specimen.
Goat Weed (Ageratum sp.), Sida Acuta, And Crotalaria Retusa As Biological Specimen.
GOAT WEED (AGERATUM SP.)
Goat weed has light blue inflorescence and is surrounded by two to three green bracts.
The life cycle extends beyond two years (continuing to flower and fruit each year).
It is an angiosperm/flowering plant and herbaceous because it has a non-woody stem.
Goat weed is also a dicotyledonous plant
- It belongs to the Class Dicotyledoneae
Reasons:
- Presence of taproot
- Presence of leaf stalk
- Presence of net venation
- Presence of broad leaves
- Presence of floral leaves in five parts
Leaf classification:
- Arrangement: opposite
- Type: simple
- Shape: ovate
- Margin: toothed.
- Tip: acute
- Base: obtuse
- Stalked /petiolate leaf
Observable features in goat weed
- Opposite Leaf arrangement
- Simple leaves
- Broad leaves
- Toothed leaf margin
- Net venation of leaves
- Hairy leaves
- Leaf possesses a stalk
- Axillary and terminal buds
- Nodes
- Long internodes
- Hairy stem
- Taproot and lateral roots
- Inflorescence or
- Capitulum collection of many small flowers or florets
- Long peduncle/flower stalk
- Pappus (calyx reduced to pappus)
Economic importance of goat weed
- Source of food for farm animals, including rabbits
Features of biological interest
- Presence of pappus for wind dispersal
- Presence of a capitulum with brightly coloured petals for insect pollination
- Small flowers grouped to form a dense head/capitulum that makes the flower conspicuous
SIDA ACUTA
Scientific Classification
Division Angiospermophyta
Reasons:
- Presence of flowers
- Seeds contained in fruits
Class Dicotyledoneae
Reasons:
- Presence of taproot
- Presence of leaf stalk
- Presence of net venation
- Presence of broad leaves
- Presence of floral leaves in five parts
Leaf classification in Sida acuta
- Arrangement: alternate
- Type: simple
- Shape: lanceolate
- Margin: serrated
- Tip: acute
- Base: rounded
- Stalk: petiolate
- Stipules: present
Observable features/characteristics of Sida acuta
- Woody stem
- Nodes and internodes
- Axillary bus and terminal buds
- Taproot system
- Flowers with brightly coloured petals
- Leaves with serrated leaf margins
- Presence of stipules
Agent of pollination
- Insect
Observable Reason:
- Brightly Coloured Petals
CROTALARIA RETUSA
Crotalaria retusa is commonly known as rattlebox or devil’s bean.
The name rattle box is derived from the fact that the seeds in the mature fruit rattle when the pod is shaken.
It is classified under a group of plants known as leguminous plants, which are notable for their ability to fix nitrogen.
Observable features or characteristics
- Fruits
- Flowers
- Stem
- Leaves
- Nodes
- Internodes
- Axillary buds
- Flower buds
Leaf classification in Crotalaria sp.
- Arrangement: alternate/spirally arranged
- Type: simple
- Shape: oblanceolate or obovate
- Margin: entire
- Tip: retuse (obtuse)/rounded
- Base: acute or cuneate
- Stalk: slightly petiolate/sessile
Describe the reproductive structure
- The flower is bisexual
- The corolla is made up of five coloured petals, the largest one, called the standard, has lines on the inner surface called honey guides which direct insects towards the nectaries
- Two side petals, called wing petals, on which the insect lands.
- Two fused petals, called the keel, enclose stamens and carpels.
- The flower stalk attaches the flower to the plant and supports it for pollination
Pollination in Crotalaria retusa
- Crotalaria is pollinated by bees
- The flower is bisexual, but the male structure matures before the female, hence encouraging cross-pollination.
- The corolla is made up of five coloured petals, the largest one, called the standard, has lines on the inner surface called honey guides which direct insects towards the nectaries
- Two side petals, called wing petals, on which the insect lands.
- Two fused petals, called the keel, enclose stamens and carpels.
- Stamens mature before stigma, thus shedding pollen into the sac-like tube of the keel.
- When a bee lands on the wing, in order to feed on nectar, its weight depresses the wing thereby opening the wing and keel.
- Pollen oozes out and dust the hairy under surface of the bee as it tries to feed on nectar.
- When the insect visits another flower, whose stigma is mature in order to get more nectar,
- Pollen from the body may stick to the sticky surface of the stigma leading to cross pollination.
Fruit classification in Crotalaria sp.
- It is a Legume
- True fruit
- Simple fruit
- Dry dehiscent fruit.
- It has marginal placentation:
- Bilaterally symmetrical
- Dry pericarp (Sutures that split open for dispersal)
Mode of dispersal
- Self/ explosive mechanism
Describe the mode of dispersal
- The method is Mechanical dispersal or explosive mechanism.
- Unequal drying of the pericarp of the fruit creates tension,
- This causes the wall of the fruit to split open into two halves along lines of weakness
- And the seeds catapulted/thrown away from parent plant thereby bringing about dispersal
Economic importance of legumes
- Fix nitrogen to the soil
- Cover crop to reduce erosion
- Fodder for animals
- Source of protein
- Used as organic manure
- Source of income
Describe a twig of Crotalaria
- Nodes and internodes present.
- Axillary buds and terminal buds.
- Axillary buds in the angle of leaves are dormant
- Simple leaves with smooth upper surface and hairy lower surface (lower surface has fine hairs)
- Sessile leaves (reduced petiole)
- Leaves are spirally arranged
- Leaves are obovate
- Tip of leaves are round or retuse
- Inflorescence at the tip of stem
- Each flower is bisexual
- The corolla is made up of five coloured (yellow) petals, the largest one called the standard, has lines on the inner surface called honey guides which direct insects towards the nectaries
- Two side petals called wing petals on which the insect lands.
- Two fused petals called the keel enclosing stamens and carpel.
- The flower stalk attaches the flower to the plant and supports it for pollination.
