Your attributes change drastically as you reach maturity.  You must spend at least two points in each of Strength and Charisma.  Your attributes will increase as you age at levels 2, 3, 10, and 18.

Plant people mature from just a few weeks to months and can live hundreds of years.  Progress occurs according to the following table.
(table shows cumulative values)

At level 1 you are just old enough to be aware of your surroundings and to uproot and move.  You appear to be a bush that walks.

At level 2 you grow into a sapling, you have reached adolescence.  You resembles a woody shrub who's branches twist together to form a humanoid-looking body with a head and limbs standing between 3 and 5 feet in height.  Your Strength increases by 5, dexterity increases by 4, and constitution increases by 2.

At level 3 you mature, you have reached adulthood.  You resemble a hunched humanoid ranging from 5 to 10 feet tall and sprout clumps of conifer like needles that quiver as you move about.  Your attributes are further increased; strength increases by 6, constitution increases by 2, intelligence and wisdom each increase by 1, and charisma increases by 4.

At level 10 you are now an elder of your race.  You resemble a humanoid with plants sprouting from them, you are have grown to 10 to 15 feet tall with small branches sprouting from your arms and shoulders, and are considered a large creature.

At level 18 you are considered an ancient tree person.  Your legs are like tree trunks, your arms have smaller branches that are thicker than most humanoids, you stand at 15 or more feet tall, and are now a huge creature.

Plant people are as varied in alignment as those capable of creating living plants.

Plant people are aware enough to adventure as a seedling when they are still small. As they reach sapling they grow to medium size.  They continue to be medium size into maturity, and in later years can frequently grow to be huge.

Your base walking speed is 30 feet.

You can sense 60 feet in all directions, but you are blind to everything beyond this range until you reach level 7.  Due to your lack of eyes and ears, you are immune to blinding and deafening.

While you remain motionless you are indistinguishable from a normal plant, which is only helpful if you are surrounded by plants of comparable size.

While not wearing armour your bark adds your Constitution bonus to your Armour Class. You are resistant to Piercing damage, vulnerable to Fire, and eventually develop Resistance to Bludgeoning damage as well.

You can use your natural abilities to attack your enemies.

You absorb nutrients through your foot like roots and require a day/night cycle of bright light and darkness for 4 or more hours each.  For each 24 hours that you do not have either 4 hours of bright light or 4 hours of darkness you gain one level of Exhaustion.  To recover this Exhaustion requires 4 hours of the missing cycle.  You also do not sleep but do require 4 hours of motionless rest each 24 hours, you may either take this rest rooted in dirt or 'eat' nutrients.  You are not affected by poisons and disease the same as mammals but are susceptible to different substances, for example simple salt is poisonous to you.

You can understand Common and another language of your choice, but are unable to speak until you reach maturity at level 3. You also have the natural ability to speak with other plants.