The same plant species can grow/develop differently depending upon the circumstances.
The root system of a sword will develop according to the nutrients, but in general each species will have similar root systems. They will spread out if given adequate room, and Echinodorus need a good deep and lateral substrate to do this for the best growth of the plant.
The leaf growth will depend also on nutrients but equally on light. Under brighter light the leaves of many Echinodorus species will be smaller.
So it makes absolutely no difference how big the plant is when you acquire it; if you were to buy one potted at 8 inches and one non-potted at 12 inches, of the same species, say E. bleheri, both will grow to exactly the same leaf size and root system in the same aquarium. In another thread I mentioned the cost difference between potted and non-potted plants; as the potted are normally much higher in cost, I seldom buy them, preferring the non-potted which even though having smaller root systems, will I know grow just as well in the proper environment.
One other comment on plants grown emersed versus submersed, which was mentioned by Harri in another thread. Plants which are bog plants in nature, as are all Echinodorus, spend half the year under water (submersed) and half in the air (emersed) with the roots perpetually in "water" whether bog, marsh, or streambed. All species adapt to permanent submersed conditions (in the aquarium) so this has no impact on whether or not they will live in the aquarium. Nurseries prefer growing these plants emersed because it is faster and therefore less expensive. I've mentioned elsewhere about plants assimilating CO2 from air four times faster than they can from water. So with comparable light and in the air the plants will grow four times faster, which means the nursery can sell them four times quicker and that means saving money. However, be prepared for a very different looking plant in your aquarium.
The emersed leaves are different from submersed leaves in their structure. But while that just occurs and basically has no bearing for the aquarist, the difference often extends to the shape and size of the leaf. That is why when you buy swords from the store or online that were grown emersed and you plant them in the aquarium fully submersed, the existing leaves usually die and new growth will be sometimes vastly different. This is one reason why identification of aquarium plants can be tricky; sometimes only the flower can be used to identify the exact species.
The intensity of light can also affect leaf shape and size. With Echinodorus, generally speaking brighter light means smaller leaves; this is especially true of the pygmy chain sword species like E. tenellus and E. quadricostatus. It also affects the red leaf species, most of which are nursery hybrids. Brighter light is required to keep them bright red because red leaves appear red due to reflecting red light, so they need more of it to photosynthesize.
Last edited by Byron; 01-31-2010 at 01:05 PM..