First True Leaves: Acer Seedling Leaf Development

This is the start of ongoing documentation into the growth and development of newly germinated maples. Species are only strongly ‘suspected’ because I collected seedlings after germination (but before true leaves had formed) from the ground underneath the supposed (but technically not necessarily) parent tree. Hybridization possibility is also not known, which is especially interesting in the case of the Japanese Maples, where all three, very distinct, seedlings came from the same tree.

All measurements shown are in centimeters. Everything grown in potting soil, watered regularly, and at least 4 hours a day of direct sunlight (ie. not natural conditions) indoors.  Since germination occurred outdoors, soil at that stage varied greatly.

[Suspected] Norway Maples (Acer platanoides)

All first leaves are unusually smooth edged compared to the average first leaves appearing outside. Soil/wind/predation differences might impact leaf shape.

Specimen 1: Age of first true leaves: 5 weeks. Height of hypocotyl above soil level: 1.8cm, somewhat straight. Length of cotyledons: 3cm, 2.5cm (beginning to wilt). Length between cotyledons and first petioles: 1.5cm. Length of petioles: 1.5cm, 1.5cm, separated by approximately 110 degrees. Dimensions of first true leaves: 3cm long x 2cm widest, 3.5cm long x 2cm widest. Deep red/burgundy hypocotyl up to cotyledons. First petioles & stem are light green with very fine hairs visible. Cotyledons are green with a green/burgundy underside. First true leaves are green on top, cordate, green underneath.

Specimen 2: Age of first true leaves: 5 weeks. Height of hypocotyl above soil level: 1cm, somewhat curved. Length of cotyledons: 3cm, 2.5cm. Length between cotyledons and first petioles: 1.5cm. Length of petioles: 2cm, 2cm, separated by approximately 120 degrees. Dimensions of first true leaves: 3cm long x 2.1cm widest, 3cm long x 2cm widest. Deep red/burgundy hypocotyl up to cotyledons. First petioles & stem are green with very fine hairs visible. Cotyledons are green with a green underside. First true leaves are deep green, cordate, green underneath.

Specimen 3: Age of first true leaves: 5 weeks. Height of hypocotyl above soil level: 1.5cm, somewhat straight. Length of cotyledons: 3cm, 3cm. Length between cotyledons and first petioles: 1.4cm. Length of petioles: 1.5cm, 1.5cm, separated by approximately 70 degrees. Dimensions of first true leaves: 3cm long x 2cm widest, 3cm long x 2cm widest. Light pinky-brown-green hypocotyl up to cotyledons. First petioles & stem are green. Cotyledons are green with a green with orange underside. First true leaves are green, a little shiny, cordate with indication of lobe structure, green underneath.

Specimen 4: Age of first true leaves: 6 weeks. Height of hypocotyl above soil level: 3.4cm, somewhat straight. Length of cotyledons: 3.5cm, 3.5cm (beginning to wilt). Length between cotyledons and first petioles: 2cm. Length of petioles: 2cm, 2cm, separated by approximately 120 degrees. Dimensions of first true leaves: 5cm long x 3.2cm widest, 5.4cm long x 3.2cm widest. Light red/browny-green hypocotyl up to cotyledons. First petioles & stem are green with very fine hairs visible. Cotyledons are green with a green underside. First true leaves are deep green, cordate, green underneath.

All of the Norway Maple seedlings considered have a similar overall look:

Acer platanoides – Specimen 4

[Suspected] Red Maples (Acer rubrum)

Specimen 1: Age of first true leaves: 3 weeks. Height of hypocotyl above soil level: 2.2cm, straight. Length of cotyledons: 4cm, 3.8cm. Length between cotyledons and first petioles: 1cm. Length of petioles: .8cm, .8cm, separated by approximately 60 degrees. Dimensions of first true leaves: 3cm long x 1.7cm widest, 3cm x 1.5cm widest. Shiny, deep red/cherry hypocotyl up to cotyledons. First petioles & stem are cherry red with visible hairs. Cotyledons are green with a green underside. First true leaves are shiny, deep burgundy, cordate although not fully open, red/burgundy underneath.

Specimen 2: (bad pictures) Age of first true leaves: 2 weeks. Height of hypocotyl above soil level: .8cm, straight. Length of cotyledons: 3.8cm, 3.5cm. Length between cotyledons and first petioles: .4cm. Length of petioles: .2cm, .2cm, separated by approximately 10 degrees. Dimensions of first true leaves: 2cm long x 1cm widest, 2cm x 1cm widest. Shiny, deep red/cherry hypocotyl up to cotyledons. First petioles & stem are orangey red with visible hairs. Cotyledons are green with a green underside. First true leaves are deep red with hints of green, not fully open, red/green underneath.

Red Maple seedling:

Acer rubrum – Specimen 1, first true leaves partially open.

[Suspected] Japanese Maples (Acer palmatum)

Specimen 1: Age of first true leaves: 3 weeks. Height of hypocotyl above soil level: 3cm, curved. Length of cotyledons: 2.5cm, 2cm. Length between cotyledons and first petioles: .3cm. Length of petioles: 1cm, 1cm, separated by approximately 70 degrees. Dimensions of first true leaves: 1.5cm long x 1cm widest, 3cm x .8cm widest. Rich red hypocotyl up to first petioles. First petioles a pink orange to light green with a light green intersection at the stem. Cotyledons transition between burgundy and green, rich burgundy underneath. First true leaves look somewhat lobed and doubly serrate (but have suffered no physical damage) green and have fine hairs visible along the central vein, green underneath but central vein visible below is slightly pink in colour.

Specimen 2: Age of first true leaves: 3 weeks. Height of hypocotyl above soil level: 3cm, straight. Length of cotyledons: 2cm, 2cm. Length between cotyledons and first petioles: None visible. Length of petioles: .8cm, .8cm, separated by approximately 70 degrees. Dimensions of first true leaves: 3cm long x 4cm widest, 3cm x 4.4cm widest. Cherry red hypocotyl up to cotyledons. First petioles are light green with a tint of orange. Cotyledons are dark green with a little burgundy, green transitioned to burgundy underneath. First true leaves are palmately lobed in green with orange-brown speckling on the top and fine hairs visible along central vein (green with pink central vein underneath).

Specimen 3: Age of first true leaves: 3 weeks. Height of hypocotyl above soil level: 3.5cm, mostly straight. Length of cotyledons: 2cm, 2cm (damaged). Length between cotyledons and first petioles: 2.1cm. Length of petioles: 1.5cm, 1.4cm, separated by approximately 70 degrees. Dimensions of first true leaves: 4cm long x 2cm widest, 4cm x 2cm widest. Light green/orange hypocotyl up to cotyledons (lightest/least orange near the cotyledons). First petioles and stem are light green with a tint of orange with visible hairs on petioles. Cotyledons are green, green underneath. First true leaves are cordate, light green, fine hairs visible along edge of leaf (none visible along veins), leaves are concave down (light green underneath).

Added: Specimen 4 (from same location/potential parentage as previous three seedlings): Age of first true leaves: unknown.

First True Leaves vs. Second True Leaves:

[Suspected] Norway Maples (Acer platanoides) Specimen 5: Age of first true leaves: 8 weeks. Height of hypocotyl above soil level: 1.8cm, straight. Cotyledons wilted. Length between cotyledons and first petioles: 2cm. Length of first petioles: 1cm, 1cm, separated by approximately 120 degrees. Dimensions of first true leaves: 3cm long x 2cm widest, 3cm x 2.1cm widest. Length between first and second petioles: 2.4cm. Length of second petioles: 2cm, 2cm, separated by approximately 90 degrees. Dimensions of second true leaves: 5cm long x 3cm widest, 4.5cm x 3.2cm widest. Red hypocotyl up to cotyledons. Petioles & stem are light green. First true leaves are green, neither cordate nor lobed, with fine hairs visible along leaf edge, green underside. Second true leaves are lighter green, several lobes (although not well defined), fine hair visible along leaf edge and top surface, green underside.

First True Leaves:

Second True Leaves: