2/7/2008
Seed Structure
Grass Seed
• Collection of cleaned, mature florets
Matured Florets
Flowering Floret
• Grass Flower
– Three stamens
• Each with one anther and
one stigma
– One ovary
– Two feathery stigmas
– Two lodicules at the base
Bluegrass Fescue
Ryegrass
Bentgrass
• Two bracts
– Palea and lemma
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Matured Floret
• Two bracts enclose the fruit
– Caryopsis developed from the ovary
Caryopsis
• Dry fruit
• Ovary wall (pericarp) fused to seedcoat
Caryposes
Spikelet
• Florets attached by its base (callus) to the
rachilla
• Two bracts (glumes) at lower end of the
spikelet
Fescue
Bluegrass
Bentgrass
Spikelet
• Bentgrass: one floret and two glumes
• Ryegrass: up to 20 florets and one glume
Inflorescence
• Spikelet borne in
inflorescence
Open
Compressed Spike
Panicle Panicle
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Inflorescence
“Floret” Identification
• Transition from vegetative to floral growth
and development
– Stem elongation
I fl
Inflorescence
Floret Directions
• Front view
– Palea is facing toward you.
– Rachilla is seen arising from the callus base.
• Side view
Rachillae
• Stem-like segment
– Protrudes up from the callus on the palea side
– Missing in bentgrass floret
– Side of the lemma is seen as it curves about the
palea.
• Back view
– Lemma faces toward you
Bluegrass Fescue Ryegrass Bentgrass
Nerves on Lemma
• Lateral nerves along the edges of the
lemma
• Mid-nerve running down the middle of
the lemma from apex to base
base.
Awn
• Arise from the mid-nerve halfway from
apex to base.
– Absent in the bluegrass.
Fescue Ryegrass Bluegrass Bentgrass
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Pubescence (hairs) on the floret
• Types
– Wispy masses to
individually spaced
stiff hairs.
Seed Identification
• Location
L
i
– At the base, on the
lemma, or along any of
the nerves.
• Maybe lost during
cleaning
Ryegrasses and Fescues
• Largest florets
– 6mm average length
Ryegrasses and Fescues
• Sample Size: 10 florets
• Magnification: Hand lens
Ryegrasses and Fescues
• Ryegrass rachilla
– Wide and flattened
against the palea.
– Oblong
g top
p
• Fescue rachilla
– Narrow cylindrical
– Circular upper end
and somewhat flared
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Ryegrasses and Fescues
• Floret Shape
– Ryegrass rectangular appearance
– Fescue somewhat elliptical
Ryegrasses and Fescues
• Inflorescence
– Ryegrass spikes
– Fescue panicels
• Spikelets
p
– Ryegrass 6-20 florets
– Tall fescues 6-8 florets
– Fine fesuce 4-7 florets
Ryegrasses
• Long, slender awn on
annual ryegrass
Bluegrasses
• Medium size floret
– 2.5 mm average length
• Fine Fescue
Fescues
• Tall fescue
– Wide and flattened
front to back
– Awn may be present
– Narrow and cylindrical
– Floret arches away
from the palea side
– awn appears as a
narrowed extension of
the whole lemma
Bluegrasses
• Sample size: 25 florets
• Magnification: hand lens or dissecting
scope
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Bluegrasses
Bluegrasses
• Inflorescence
– Open to compressed panicles
– 2 to 3 florets per spikelet in rough bluegrass
– 3 to 6 florets in other species
Poa
annua
Bluegrasses
• Canada bluegrass
– Smooth lemma
• No visible intermediate nerves
– Widening of the lemma above the middle
Bluegrasses
• Kentucky bluegrass
– Pubescence completely
removed
– Lemma edges tend to
curve
– Lemma edges wrapped
more weakly about the
palea
Poa
compressa
Poa
pratensis
Poa
trivialis
Bluegrasses
• Rough bluegrass
– Remnant of basal
pubescence
– Prominent intermediate
nerves
– Lemma straight along
its edges
– Edges of the lemma
folded over the palea.
Bluegrasses
• Annual bluegrass
– Very prominent intermediate,lateral and midnerves
– Pubescence may be seen along any or all of
these nerves in abundance
– Palea and lemma appear to be sucked in tightly
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Bentgrasses
• Very small florets
– 1.5mm average in length
Bentgrasses
• Can be difficult to identify
• Sample Size: 50 florets
Bentgrasses
• Inflorescence open or compressed
Agrostis
alba
Agrostis Agrostis Agrostis
Cania
palustris tenuis
Bentgrasses
• Spikelet
– One floret and two glumes
• Typical bentgrass sample
– May contain several spiklelets
• Size, color, retained pedicels
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Bentgrasses
• Velvet bentgrass
– Most awns entact
• Bent awn, arsing from mid-rib about one half of the
wayy from base to apex
p
• Five nerves below awn’s point of attachment, four
above.
Bentgrasses
• Colonial bentgrass
– Shiny paleas and lemmas
– 3 or 5 nerves visible
– Variable length
g of p
palea Stiff hairs arising
g from the
lemma surface
– Awn originating from near the callu
– Palea is rudimentary
– Lemma grainy
Bentgrasses
• Creeping bentgrass
– Awn rarely present
• Remaining stub on the mid-nerve toward the apex.
–
–
–
–
5-nerved lemma is more often
Palea longer than the caryopsis
Stubby basal hairs
Shinny bract
Bentgrasses
• Redtop,
–
–
–
–
Difficult to distinguish from creeping BG
More often 3-nerved
Usuallyy longer
g basal hair
Palea as long as the caryopsis
Seed Identification
• Many varieties deviate in floret phenotype
(outward physical characteristics) from the
norm for that species
Seed Quality
• Purity
– Percentage of pure seed of an identified
species or cultivar
– Remaining percentage
• inert matter, weed seeds, and other crop seeds
• Viability
– Percentage of seed that is alive and will
germinate under standard conditions
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Seed Quality
Seed Quality
• Pure Live seed (PLS)
• Product of purity and viability
– 92% Purity x 80 %Viability = 73.6 % PLS.
• Compare seed prices
Actual cost of pure live seed = Cost per pound of seed x 100
PLS %
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