The threepenny piece has the plant Thrift.
Thrift is known as tonna chladaich in Gaelic which means beach wave. In Welsh, it is called clustog fair, meaning Mary's pillow. Thrift was used as an emblem on the old 12-sided threepenny coin as a reminder of the importance of spending money wisely during the wars.
The half penny was the Golden Hind.
And the Lady on the penny was,
Britannia
Since her reappearance in 1672, Britannia has never been absent from the nation's coins. Over the years she became more and more associated with the sea. On the famous cartwheel pennies and twopences of 1797 she was shown seated on rocks in the sea, with a ship in the background and her spear replaced by a trident.
I do find it remarkable, when looking at the old pre-decimal coinage, to remember how big the coins were when compared to the later, decimal ones.
Some more Trivia: As a school kid in the 60's, I remember being tought that some of the coins also could be used as weights and measures.
The halfpenny had a diameter of an inch, so 12 of them (sixpen'orth) laid in a line would measure one foot.
The penny, it weighed one third of an ounce, so three equalled one ounce.
It appears that old pennies are still used to regulate the Elizabeth Tower Clock (sometimes erroneously referred to as Big Ben). Apparently, adding one penny causes the clock to gain two-fifths of a second in 24 hours.