Seed Morphology Flashcards
Arils
- derived from faniculus (maternal tissue) - function: attracting dispersal animals
Axial embryo morphology
2 Types: - endospermic seeds
- Linear:
- embryo is longer than it is wide
- cotyledons are not wider than the embryo axis
- straight or curved or coiled
- in gymnosperms, dicots, or monocots - Miniature:
- embryos are small and often undifferentiated
- very little nutritive tissue
- seed size is often tiny like dust
- in monocots and dicots
- many epiphytic or parasitic
- all orchids
Basic embryo types
- 12 types: - 4 Basal (Rudimentary, Broad, Capitate, Lateral) - 1 Peripheral - 2 Axial (Linear (straight or coiled), Miniature) - 4 Foliate (Spatulate, Investing, Bent, Folded)
Caruncle
- elaiosome in the euphorbia family - in castor bean - spongy outgrowth of outer seed coat - covers the hilum and micropyle - function: absorbing water for germination
Caryopsis
- ‘seed’ of grasses - actually a fruit - pericarp and seed coat are fused to form a single seed - dry, indehiscent fruit - ex: corn
Chalazasperm
- type of seed storage tissue - least common type - diploid (2n) - derived from the chalazal region in the ovule - (chalazal region is the opposite side of the seed from where the micropyle entered)
Elaiosomes
- specialized seed arils - nutrient-containing organs (especially oils) specifically designed to attract ants - ants use the elaisome as a food source, and plant benefits by ant dispersal of seed (called myrmecochory) - usually derived from outer layer of seed coat
Endospermic seeds
- seeds where endosperm is the main storage tissue - Basal & Axial embryo types - in most angiosperms: - endosperm is triploid (3n) tissue - derived from fusion of 1 sperm & 2 egg cells during double fertilization - ex: carrot - in gymnosperms: - endosperm is haploid (1n) - derived from female gametophyte - ex: gingko, pine
Foliate embryo morphology
4 types: - all have very little endosperm - during development, made endosperm but got all used up making cotyledons (which are now the nutritive tissue) - non-endospermic seeds 1. Spatulate: - wide, flat cotyledons - cotyledons occupy most of the center of the seed - only in dicots 2. Investing: - like Spatulate - but cotyledons are thick and overlap the short axis - only in dicots 3. Bent: - “jack-knife” appearance - embryo turns inside the seed - cotyledons fill most of seed - only in dicots (legume, mustard, cashew families) 4. Folded: - wide cotyledons that are folded and appear wavy in seed - only in dicots (maple, geranium families)
Integuments
- the tissue originally surrounding the ovule - is derived from maternal plant tissue (so genetically identical to mother plant and genetically different from embryo) - forms the seed coat - can differentiate into layers with different morphological properties
Mucilage
a sticky gelatinous substance exuded and surrounding seed upon hydration.
Myrmecochory
- a strategy for seed dissemination by ants - elaiosomes rich in oils and other nutrients attract ants as reward for ant dispersal
Non-endospermic seeds
- seeds where cotyledons fill entire seed - cotyledons act as food reserve - little to no endosperm - had endosperm but was used up during development - cotyledons came from embryo so diploid (2n) - Foliate embryo types - ex: bean
Pericarp
-ovary tissue - fruit parts that cover the seed
Peripheral embryo morphology
1 type: - embryo grows along edge of seed - embryo surrounds perisperm (nutritive tissue) - in one dicot order: Caryophyllales (includes cactus, amaranth, knotweeds, purslane)
Perisperm
- inner nutritive tissue - diploid (2n) - derived from the nucellus (female) - but has different genetic tissue b/c never went through meiosis - in Peripheral Embryo Type, the embryo grows around the perisperm
Plumes of hairs
- usually to aid in wind dispersal - hairs can derive from outer seed coat - ex: rose of Sharon - hairs can form from flower tissue (anthrocarp) - sepals (calyx) forms a tuft of hairs (bristles) called pappas - ex: composites (Asteraceae)
Sarcotesta
- outer seed coat layer - remains living - is fleshy at maturity - soft - usually to attract something for dispersal - in 17 angiosperm families (magnolia, cycads)
Seed Coat
- derives from integuments - not just a shell, pretty complex - can have specialized cells like : macrosclereids, sarcotesta, - outer surface can have various textures and shapes (waxes, seed hairs, wings, protuberances, stomata, elaisomes, mucilage, arils)
Wings
- flattened extension along the periphery of seed - derived primarily from integument (seed coat)
Diaspore
- Not just the botanical seed, but the reproductive unit. - The smallest part of the reproductive unit - mature ovule - The smallest unit of dispersal for the next generation - so can include parts of ovary (fruit) and flower parts. (ex: samara) - ex: acorn is diaspore because it is the smallest unit we plant.
Basal embryo morphology
4 types: 1. Rudimentary: - tiny embryo at base of seed, huge endosperm - small but discernible cotyledons - primitive evolutionary condition - in monocots & dicots 2. Broad: - tiny undifferentiated embryo at base of seed, huge endosperm - in select monocots (rush & water lily families) 3. Capitate: - tiny undifferentiated embryo with spreading cap at base of seed, huge endosperm - in selected monocots (sedge & spiderwort families) 4. Lateral: - embryo pressed against one side of seed, huge endosperm - in monocots - grasses - like corn
True Seed
- ripened ovule - consists of: - an embryo - stored food supply - a protective covering - sexual reproductive unit in plant
types of seed storage tissue
- Endosperm 2. Cotyledons (non-endospermic) 3. Perisperm 4. Chalazasperm
what are the major storage reserves in seeds
- Proteins 2. Carbohydrates (starch) 3. Lipids (oils)
Aleurone cells
- secrete enzymes that digest endosperm - ex: in corn
Macrosclereids
- Malpighian cells - specialized outer palisade layer of cells - in seed coat of seeds w/ physical dormancy - are very hard
