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• Aristida tuberculosa

Aristida tuberculosa — seaside threeawn

Facts

Seaside threeawn is a plant of coastal sand dunes in New England. It has notably unusual awns that are loosely twisted around one another at the base. This is a great illustration of functional morphology, as the awns remain attached to the caryopsis (fruit) after dispersal, and function to bury the caryopsis in the sand as the awns twist and untwist with changes in humidity.

Habitat

Anthropogenic (man-made or disturbed habitats), dunes, grassland, meadows and fields

Characteristics

• Flowers

  Anther number

  3

  Awn on glume

  the glume has an awn

  Bristles below spikelets

  no

  Floret lower bract texture

  the lemma is hard and firm

  Floret number

  1

  Floret types within spikelet

  all the florets within a spikelet are similar

  Glume awn length

  5–10 mm

  Glume relative length

  one or both glumes are as long or longer than all of the florets

  Glume veins

  1

  Glumes per spikelet

  2

  Inflorescence arrangement

  the spikelets are uniform

  Inflorescence axis orientation

  the inflorescence axis is straight

  Inflorescence branch length

  1–4 cm

  Inflorescence branches

  the flowers are attached to branches rather than to the main axis of the inflorescence

  Inflorescence crowding

  • the panicle is somewhat to very congested (crowded), and the branches may not be clearly seen without close inspection
  • the panicle is somewhat to very spread out, with clearly-evident branches

  Inflorescence length

  100–200 mm

  Inflorescence length to width ratio

  2–3.3

  Inflorescence type (general)

  the spikelets are borne on stalks or on branches

  Inflorescence type (specific)

  the inflorescence is branched, and the branches do NOT both grow from the same side of the plant AND look like spikes

  Inflorescence width

  30–100 mm

  Inforescence position

  the spikelets are mainly carried at the end of the stem

  Lemma awn base

  the awn is attached right at the tip of the lemma

  Lemma awn coiled

  the lemma awn is coiled at least one half turn

  Lemma awn length

  38–55 mm

  Lemma awn number

  the lemma has more than one awn on it

  Lemma awn orientation

  the awn of the lemma on dried or older plants is curved or bent outwards

  Lemma base hairs

  the lemma has hairs at the base

  Lemma base length

  3–4 mm

  Lemma cross-section

  the lemma is flat or rounded if you cut across the midpoint

  Lemma surface

  the surface of the lemma is relatively smooth (not counting any longitudinal veins or hairs)

  Lemma tip

  the lemma tip is a simple point, with or without an awn (long narrow extension ending in a point)

  Lemma vein number

  3

  Lower glume length

  20–30 mm

  Lower glume relative length

  the lower glume is nearly as long, or as long as, the upper glume

  One or more florets

  there is one floret per spikelet

  Palea relative length

  palea is one half to fully as long as lemma

  Reproductive system

  all the flowers on the plant have both carpels and stamens (synoecious)

  Spikelet axis tip

  there is no extension of the spikelet axis beyond the tip of the spikelet

  Spikelet disintegration

  the spikelet breaks off above the glumes, so that after the florets fall off, the glumes remain

  Spikelet length

  6–12 mm

  Spikelet number per node

  0

  Spikelets per panicle branch

  1–4

  Spikelets spiny

  the spikelets do not appear spiny

  Tip of glume

  the tip of the glume is not divided (though it may have an awn on it)

  Upper glume length

  20–30 mm

  Upper glume relative length

  the upper glume is more than one half as long as the lowest lemma

  Upper glume shape

  the upper glume is widest at or below the middle

• Fruits or seeds

  Seed length

  8–10 mm

• Growth form

  Horizontal rooting stem

  no

  Lifespan

  the plant lives only a single year or less

  Rhizomes

  no

  Roots

  there are only slender roots on the plant

• Leaves

  Basal leaves

  the plant has few or no leaves coming from the base of the flowering stem

  Leaf auricles

  the leaves do not have auricles

  Leaf basal lobe hairy

  NA

  Leaf blade cross-section

  the leaf blade is more or less flat in cross-section, or slightly folded or rolled inwards

  Leaf blade hairs

  the leaf blade is hairless, but it may have tiny prickles that give it a sand-papery feel

  Leaf blade length

  8–25 cm

  Leaf blade texture

  • the leaf blade is rough and sandpapery
  • the leaf blade is smooth, or it may have soft hairs

  Leaf blade width

  2–4 mm

  Leaf ligule type

  the leaf ligule is in the form of fine hairs

  Leaf margin glands

  there are no glands along the edges of the leaf blade

  Leaf sheath closed around stem

  the margins of the leaf sheath are overlapping and not fused together except in the basal half (or less)

  Leaf sheath hair type

  • there are hairs on the surface of the leaf sheath, but the hairs do not have blisters at their bases
  • there are no hairs on the surface of the leaf sheath

  Leaf sheath hairs

  • there are hairs on the surface of the leaf sheath
  • there are no hairs on the surface of the leaf sheath

• Place

  Habitat

  terrestrial

  New England state

  • Connecticut
  • Massachusetts
  • New Hampshire

  Specific habitat

  • dunes
  • grasslands
  • man-made or disturbed habitats
  • meadows or fields

• Stem, shoot, branch

  Hairs at nodes

  the stem nodes are hairless or they have very sparse hairs

  Plant height

  25–100 cm

  Stem hairs

  the stem is nearly to completely hairless

  Stem orientation

  • the stems are upright
  • the stems trail at the base, but turn upwards at the tips

  Stem spacing

  the stems grow close together in compact clusters or tufts

Wetland status

Not classified

New England distribution and conservation status

From the dichotomous key of Flora Novae Angliae