Hello Sandra,

Sorry this response took so long.  I wrote one already and forgot to push "send"

Your podocarpus macrophyllus looks as if it is suffering from overwatering.  

Does your pot have a drainage hole?  If it doesn't, then you need to repot it in a pot that does have one.  When water sits at the bottom of a houseplant's pot, it is an invitation for root rot.   In any event, I would gently knock the pot, remove the plant and inspect the roots.  You will be able to tell if any have rotted.  These should be cut off, leaving only healthy roots.

The watering instructions for potten podocarpus online is to water only when the top 2" of soil is dry.  You can buy a moisture meter at garden centers or online to help you determine that.

It is also stated that these plants are relatively drought tolerant, so dry soil is better than soggy soil.  You do not want the plant to dry out  totally.

With a drainage hole in place, you will need a saucer underneath.

To water the plant, place it in the sink or a large bowl, water and then let the extra water drain.  Or if it is too heavy, use a turkey baster to suck up the excess water from the plant saucer. You do not want water sitting in the saucer.

Check your potting soil.  you might want to amend with some light potting soil that will help drainage.  This soil needs to be dampened with warm water when repotting but will drain well.

I realize that this a lot of trouble, but a lot of house plants do not like soggy pot bottoms...

Lastly, I am hoping that the darkening of the stem is from age not root rot.  You will determine that by inspecting the roots.