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Baby Leaves

All plants have seed leaves. These are the leaves which occur in the seed. Flowering plants fall into two big groups: the Dicotyledons (say die-cot-a-lee-don) (two-seed-leaves) and Monocotyledons (one-seed-leaf). Pine trees and many other Gymnosperms can perhaps be called polycotyledons (many-seed-leaves). Since all proteas have two seed leaves they are Dicotyledons or, in short, Dicots.

But some proteas have baby leaves as well. Take the Silky Needlebush, Hakea suaveolens. It has adult leaves which are divided! Of the three Needlebushes threatening our proteas, it is the only species with divided leaves. But most Hakeas have large flat leaves (the other two of our needlebushes are not typical Hakeas!). How then did the Silky Needlebush get divided leaves? The answer is simple: look at the baby leaves - the first few leaves growing after the seed-leaves pop out of the seed. From these oval leaves grow little pimples which get longer and longer until they form long-thin needles. Neat hey!

And while you are looking at aliens, take a look at those other invaders, the Acacias. Acacia cyclops, saligna, longifolia and melanoxylon all have broad flat leaves. Except that they are not really leaves! They are in fact leaf stalks! Look at a baby Acacia which has just hatched (OK, germinated): it has feathery leaves. And the next leaf is less feathery and the stalk gets bigger, and the next has very few "feathers" are a larger stalk, and the next has no feathers at all, just a big flat stalk. The Blackwood Acacia melanoxylon makes feathery "baby-leaves" in the shade and flat "leaf-stalks" in the sun.

Scepters (Paranomus) have done exactly the same thing, except that they do not change their leaves when still seedlings. The baby leaves are divided and some Scepters only ever produce baby leaves. A section in the genus decided that baby leaves are not for mature plants! So just before they flower they produce "adult leaves" And how have they done this? They have flattened the leaf lobes just like the Acacias to produce heart-shaped or oval leaves. But, long ago, when Scepters changed their flat leaves to needle-leaves they forgot how to connect the veins in the leaf - in a needle leaf cross-veins are not important. Most Dicots have net veins to make sure that if a leaf is broken or torn, fine veins form a net that can get water to all the leaf and take food away from it to the rest of the plant. Because scepters have forgotten how to make net veins they only have straight veins without any connections. This is why they were given the name Paranomus which means "beside the custom" - the custom being "net veins" which most other Dicots have.

Another Dicot genus Corymbium (a daisy) did exactly the same thing: many hikers mistake its leaves for lily leaves. It is thought that the ancestor of Monocots also changed to needle-leaves and forgot how to make net veins! But Monocots figured out another way and between their "parallel veins" are little "cross veins" (like steps on a ladder) which allow food and water to get to damaged bits of leaf.

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