Explain distinguishing characters of Dipterocarpaceae, Asteraceae and Orchidaceae.

Dipterocarpaceae

Dipterocarpaceae, commonly known as the dipterocarp family, comprises large trees predominantly found in Southeast Asia. They are ecologically vital, forming the climax vegetation of many rainforests. Key distinguishing characters include:

• Habit: Large, emergent trees, often reaching heights of 40-60 meters.
• Root: Presence of buttress roots, providing stability in shallow soils.
• Stem: Straight, cylindrical trunks with often smooth bark. Resin canals are abundant in the wood.
• Leaf: Alternate, simple, and usually entire (smooth margins). Pinnately veined.
• Inflorescence: Panicles or racemes, often bearing numerous small flowers.
• Flower: Small, inconspicuous, and usually unisexual (dioecious). Perianth is reduced.
• Fruit: A unique one-winged samara, often with a persistent calyx. This winged fruit aids in wind dispersal.
• Seeds: Typically have a wing-like structure for wind dispersal.

Asteraceae (Compositae)

Asteraceae, or the sunflower family, is one of the largest plant families, characterized by its composite flower heads. They are found in diverse habitats worldwide. Distinguishing features are:

• Habit: Highly variable – herbs, shrubs, and trees.
• Root: Taproot system is common.
• Stem: Variable, often with latex ducts.
• Leaf: Alternate, simple, or compound, often with serrated or lobed margins.
• Inflorescence: Capitulum (head) – a characteristic feature. The head consists of numerous small florets arranged on a receptacle.
• Flower: Two types of florets are present: ray florets (ligulate, with strap-shaped petals) and disc florets (tubular).
• Fruit: Achene – a small, dry, one-seeded fruit. Often with a pappus (modified calyx) for wind dispersal.

Orchidaceae

Orchidaceae, the orchid family, is a highly diverse group known for its intricate and specialized flowers. They are found in a wide range of habitats, often epiphytic. Key characteristics include:

• Habit: Epiphytic (growing on other plants), lithophytic (growing on rocks), or terrestrial (growing in soil).
• Root: Often aerial, with velamen – a spongy outer layer that absorbs moisture and nutrients.
• Stem: Reduced, often forming a pseudobulb for water storage.
• Leaf: Variable, often leathery and evergreen.
• Inflorescence: Raceme or panicle.
• Flower: Highly specialized, with three sepals, three petals, and a lip (labellum) – a modified petal that attracts pollinators. Column is present (fusion of stamen and pistil).
• Fruit: Capsule – a dry, dehiscent fruit containing numerous tiny seeds.
• Seeds: Extremely small and dust-like, lacking endosperm. They rely on fungal symbiosis for germination.

The following table summarizes the key differences:

Character	Dipterocarpaceae	Asteraceae	Orchidaceae
Habit	Large trees	Herbs, shrubs, trees	Epiphytic, lithophytic, terrestrial
Inflorescence	Panicle/Raceme	Capitulum (head)	Raceme/Panicle
Flower	Small, unisexual	Ray & Disc florets	Highly specialized, lip present
Fruit	Samara	Achene	Capsule
Root	Buttress roots	Taproot	Aerial roots with velamen