Seed Morphology

Question 1

Arils

Answer 1

• derived from faniculus (maternal tissue) - function: attracting dispersal animals

Question 2

Axial embryo morphology

Answer 2

2 Types: - endospermic seeds

1. 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
2. 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

Question 3

Basic embryo types

Answer 3

• 12 types: - 4 Basal (Rudimentary, Broad, Capitate, Lateral) - 1 Peripheral - 2 Axial (Linear (straight or coiled), Miniature) - 4 Foliate (Spatulate, Investing, Bent, Folded)

Question 4

Caruncle

Answer 4

• elaiosome in the euphorbia family - in castor bean - spongy outgrowth of outer seed coat - covers the hilum and micropyle - function: absorbing water for germination

Question 5

Caryopsis

Answer 5

• ‘seed’ of grasses - actually a fruit - pericarp and seed coat are fused to form a single seed - dry, indehiscent fruit - ex: corn

Question 6

Chalazasperm

Answer 6

• 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)

Question 7

Elaiosomes

Answer 7

• 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

Question 8

Endospermic seeds

Answer 8

• 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

Question 9

Foliate embryo morphology

Answer 9

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)

Question 10

Integuments

Answer 10

• 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

Question 11

Mucilage

Answer 11

a sticky gelatinous substance exuded and surrounding seed upon hydration.

Question 12

Myrmecochory

Answer 12

• a strategy for seed dissemination by ants - elaiosomes rich in oils and other nutrients attract ants as reward for ant dispersal

Question 13

Non-endospermic seeds

Answer 13

• 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

Question 14

Pericarp

Answer 14

-ovary tissue - fruit parts that cover the seed

Question 15

Peripheral embryo morphology

Answer 15

1 type: - embryo grows along edge of seed - embryo surrounds perisperm (nutritive tissue) - in one dicot order: Caryophyllales (includes cactus, amaranth, knotweeds, purslane)

Question 16

Perisperm

Answer 16

• 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

Question 17

Plumes of hairs

Answer 17

• 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)

Question 18

Sarcotesta

Answer 18

• outer seed coat layer - remains living - is fleshy at maturity - soft - usually to attract something for dispersal - in 17 angiosperm families (magnolia, cycads)

Question 19

Seed Coat

Answer 19

• 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)

Question 20

Wings

Answer 20

• flattened extension along the periphery of seed - derived primarily from integument (seed coat)

Question 21

Diaspore

Answer 21

• 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.

Question 22

Basal embryo morphology

Answer 22

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

Question 23

True Seed

Answer 23

• ripened ovule - consists of: - an embryo - stored food supply - a protective covering - sexual reproductive unit in plant

Question 24

types of seed storage tissue

Answer 24

1. Endosperm 2. Cotyledons (non-endospermic) 3. Perisperm 4. Chalazasperm

Question 25

what are the major storage reserves in seeds

Answer 25

1. Proteins 2. Carbohydrates (starch) 3. Lipids (oils)

Question 26

Aleurone cells

Answer 26

- secrete enzymes that digest endosperm - ex: in corn

Question 27

Macrosclereids

Answer 27

- Malpighian cells - specialized outer palisade layer of cells - in seed coat of seeds w/ physical dormancy - are very hard