Find the gymnosperm leaf

Here's some leaves that the Phactor scanned after using them in a class. They are all tropical woody plants, but none are any more closer related than being members of the same order.  Note how similar they all are in shape and with a smooth margin. They all have a bit of a short drip tip, and all have pretty waxy cuticles. Now here's the fun part - one is a gymnosperm (Gnetum), one is basal angiosperm (Illicium), and the other two are from the Magnoliales (Myristica, Eupomatia).  Can you figure it out? Hey, does the Phactor have a cool collection of plants at his disposal or what? 

This week's lab - angiosperm leaf diversity

Not only do flowering plants have a tremendous diversity of leaf shapes and forms, they are adapted to many different habitats and they have specialized for many other purposes as well.  First all those floral parts are modified leaves. Then there are all the other funky things angiosperms have done with leaves: protection, coevolution, traps, succulent leaves, vestigial leaves, climbing aids (tendrils, grappling hooks), attraction, flotation, xerophytic leaves.  Why this will be just like a leaf scavenger hunt through the glasshouse, and that's good because the weather outside is appalling: wintery mix (April 23d) at just above freezing.  Here's a nice tropical leaf with adaptations for dealing with heavy rainfall: a drip tip and vein gutters.  Both help shed water quickly.  So what plant has this leaf? 

Tropical leaf drip tips - yam

A student asked a good question the other day after telling them about past climatic differences. How do we know what the climate was like millions of years ago? One answer too frequently heard is that we can't know because no one was there to observe the climate. In the real world observations can still be made about the past. For example, leaves display different forms as adaptations to different climates. Here's a leaf from a yam (Dioscorea), which is not a sweet potato. The leaf shows a couple of adaptations for a wetter environment. First it's a fairly large leaf, and leaf size is very generally correlated positively with warmer wetter climates. Note the attenuated apical tip, a drip tip, with a drip on the tip, and like the pouring lip of a beaker or pitcher, that tip helps water drip and pour off the leaf more efficiently. The major veins that generally follow the out line of the leaf margin from base to tip form valleys, gutters, again to help water pour off the leaf. So when you find fossils with such features, or with features associated with very seasonal climates, or very dry climates, paleobotanists, infer that they were adapted to a particular climate suited to that leaf type. And if that's not so, then maybe those leaves weren't well designed after all.