And unto Adam he said, Because thou hast hearkened unto the voice of thy wife, and hast eaten of the tree, of which I commanded thee, saying, Thou shalt not eat of it: cursed is the ground for thy sake; in sorrow shalt thou eat of it all the days of thy life; Thorns also and thistles shall it bring forth to thee; and thou shalt eat the herb of the field; Genesis 3:17-18
Adam was not cursed on account of the earth, which God had declared to be in itself very good; but the earth was cursed because of the sin of Adam, which again originated in the spirit of the Evil One. As a punishment for man's transgression the soil should be henceforth comparatively barren. It should no longer yield spontaneous abundance, but he should be compelled to force out of it, with heavy toil and in the sweat of his face, even the bare necessaries of life.
Nor would this be the end of the trouble. Earth should now be the parent of evil as well as good, and, teeming with thorns and thistles, should baffle and protract the labor of its tillers.
These noxious plants probably existed, though in very different condition, before the curse was pronounced; and then, owing to the sterility of the blighted earth, were no longer able to attain to their proper development and luxuriance, and so became what they are now found to be- abortions.
The following remarks of Professor Balfour will illustrate this.
In looking at the vegetable world in a scientific point of view, we see many evidences of the great plan upon which the all-wise Creator seems to have formed that portion of His works. At the same time there are many marks of what we may call, with reverence, incompleteness. Thus we see that there is in all plants a tendency to a spiral arrangement of leaves and branches, etc., but we rarely see this carried out fully, in consequence of numerous interruptions to growth and abnormalities in development. When branches are arrested in growth they often appear in the form of thorns or spines, and thus thorns may be taken as an indication of an imperfection in the branch.
[Donna:Regarding that last sentence, it is interesting that telestial-level people in the OT are also compared to thorns, briers, and noxious weeds.]
The curse which has been pronounced on the vegetable creation may thus be seen in the production of thorns in place of branches-thorns which, while they are leafless, are at the same time the cause of injury to man. That thorns are abortive branches is we'll seen in cases where, by cultivation, they disappear. In such cases they are transformed into branches. The wild apple is a thorny plant, but on cultivation it is not so. These changes are the result of a constant high state of cultivation, and may show us what might take place were the curse removed.
[When the curse is removed, plants (and humans!) will bring forth fruit instead of thorns.]
Again; thistles are troublesome and injurious in consequence of the pappus and hairs appended to their fruit, which waft it about in all directions, and injure the work of man so far as agricultural operations are concerned. Now it is interesting to remark that this pappus is shown to be an abortive state of the calyx, which is not developed as in ordinary instances, but becomes changed into hairs. Here, then, we see an alteration in the calyx which makes the thistle a source of labor and trouble to man. We could conceive the calyx otherwise developed, and thus preventing the injurious consequences which result to the fields from the presence of thistles.
I have thus very hurriedly stated to you what occurred to my mind as to the curse of thorns and thistles, and I have endeavored to show that the spines and hairs are abortive, and, so to speak, imperfect portions of plants. The parts are not developed in full perfection like what may have been the case in Eden, and like what will take place when the curse is removed.
Fit objects, then, are the thorn and the thistle to remind man of the curse. And keeping their origin in view we can see a deep significance in that awful scene when our Lord suffered Himself to be crowned with thorns, so that even His enemies set Him forth as the great Curse-bearer ; when He wore on His bleeding brow that which owed its very existence to, and was the sign of, the sin which He had come to expiate.
Lastly; man should no longer eat of the fruits of Paradise, but should henceforth find the staff of his fleeting life in the bread-producing herbs of the field, till he himself descended into that dust out of which he obtained his food: for dust he was, and unto dust he should return.
(http://www.creationdays.dk/G%20H%20Pember/6.html)