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• Potamogetonaceae
• Potamogeton
• Potamogeton robbinsii

Potamogeton robbinsii — Robbins' pondweed

Facts

Robbins' pondweed forms large colonies in deep water. It rarely flowers, but when it does, it is distinctive for its branched inflorescence. As in a few other pondweeds (Potamogeton), its stipules are fused to the leaf blades, with only the tip of the stipule free. Maximum densities can reach 1000 plants per square meter in water between 5 and 7 meters deep.

Habitat

Lacustrine (in lakes or ponds), riverine (in rivers or streams)

Characteristics

• Clonal plantlets

  Turion length

  0 mm

• Flowers

  Anther color

  there is a noticeable pink, reddish or purplish tint to the anthers

  Carpels fused

  the carpel is solitary or (if 2 or more) the carpels are not fused to one another

  Flower lower lip length

  0 mm

  Flower position

  the flowers are below the surface of the water

  Flower symmetry

  there are two or more ways to evenly divide the flower (the flower is radially symmetrical)

  Inflorescence length

  7–20 mm

  Inflorescence type

  the inflorescence is a spike (a long unbranched stem with flowers along it that lack stalks)

  Length of flower stalk

  0 mm

  Length of peduncle

  30–70 mm

  Nectar spur

  the flower has no nectar spurs

  Number of carpels

  1–4

  Ovary position

  the sepals and/or petals are attached below the ovary

  Palate on corolla

  no

  Petal and sepal arrangement

  the flower includes only one cycle of petals or sepals

  Petal appearance

  the petals are green and/or leafy in texture

  Petal color

  green

  Petal fringed edges

  the petals are not fringed

  Petal fusion

  the perianth parts are separate

  Petal hairs on inner/upper surface

  there are no hairs on the inner/upper petal surface

  Petal number

  4

  Petal or sepal number

  there are four petals, sepals, or tepals in the flower

  Pistil number

  • 1
  • 4

  Sepal appearance

  NA

  Sepal length

  0 mm

  Sepal number

  0

  Sepals fused only to sepals

  NA

  Spur length

  0 mm

  Stamen number

  4

  Stamen position relative to petals

  NA

  Stamens fused

  the stamens are not fused to one another

  Stamens fused to petals

  the stamens are fused near the bases of the petals or tepals

  Style number

  0–4

• Fruits or seeds

  Fruit beak length

  0.7–0.9 mm

  Fruit length

  3–5 mm

  Fruit type (general)

  • the fruit is dry but does not split open when ripe
  • the fruit is fleshy

  Fruit type (specific)

  • the fruit is a drupe (fleshy, with a firm inner ovary wall that encloses a single seed)
  • the fruit is an achene (dry, usually 1-seeded, does not separate or split open at maturity)

  Fruit width

  2–3.3 mm

• Glands or sap

  Oil glands on nodes

  none of the nodes have oil glands

  Sap

  the sap is clear and watery

• Growth form

  Lifespan

  the plant lives more than two years

  Root septa

  the roots do not have transverse septa

  Roots floating in water

  there are no clusters of roots floating in the water

  Turions

  there are no turions on the plant

  Underground organs

  the plant has a rhizome (a horizontal underground stem with roots growing from it)

• Leaves

  Bract position (Sparganium)

  NA

  Bract relative length

  At least 3854 mm

  Bracts

  neither the flowers nor their pedicels have bracts

  Floating leaf basal lobes

  NA

  Floating leaf blade width

  0 mm

  Floating leaf length

  0 mm

  Floating leaf shape

  NA

  Floating leaf tip

  NA

  Floral bract form

  NA

  Floral bract length

  0 mm

  Leaf arrangement

  alternate: there is one leaf per node along the stem

  Leaf blade length

  20–120 mm

  Leaf blade veins

  the lateral veins are parallel or slightly arched in the direction of the tip

  Leaf blade width

  3–8 mm

  Leaf position

  the leaves are all submerged underwater

  Leaf special features

  none of the mentioned special features are present

  Leaf-like branch segments

  0

  Leaf-like branch shape

  NA

  Specific leaf type

  the leaf is not divided, rather the blade is made up of one segment

  Staminate bract edge (Myriophyllum)

  NA

  Stipule appearance

  the stipules are firm or fibrous, and colored white, green or brown

  Stipule fused to leaf

  the stipules are attached to the leaf blade for some part of their length

  Stipules

  the plant has stipules

  Stipules fused around stem

  the stipules do not forma closed tube around the stem

  Trap-bladder length

  0 mm

  Underwater leaf air passage number

  At least 1439

  Underwater leaf air passage relative width

  At least 4336

  Underwater leaf air passage row number

  0

  Underwater leaf blade edges

  the underwater leaf blade edges are toothed

  Underwater leaf blade shape

  • the underwater leaf blade is lanceolate (lance-shaped; widest below the middle and tapering at both ends)
  • the underwater leaf blade is linear (very narrow with more or less parallel sides)

  Underwater leaf blade veins

  20–60

  Underwater leaf blade width

  3–8 mm

  Underwater leaf length

  20–120 mm

  Underwater leaf stalk

  no

  Underwater leaf stalk length

  0 mm

  Underwater leaf tip shape

  the tip of the underwater leaf is acute (sharply pointed)

  Veins in floating leaf

  0

• Place

  Habitat

  aquatic

  New England state

  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Rhode Island
  • Vermont

  Specific habitat

  • in lakes or ponds
  • in rivers or streams

• Stem, shoot, branch

  Flowering stem growth form

  the flowering stem is upright

Wetland status

Occurs only in wetlands. (Wetland indicator code: OBL)

New England distribution and conservation status

From the dichotomous key of Flora Novae Angliae