I suppose I should check these things out more thoroughly.
The consensus in the news reports is that Prime Minister Abe sent a sakaki, a very nice dark-leaved plant of the camellia family used in Shintō religious ceremonies, to Yasukuni Shrine for the Spring Festival. Or sponsored the presentation of said plant to the Shrine.
However, the original reports I read had the Prime Minister sending/sponsoring a masakaki ---which a a rather different and I think more significant thing.
A masakaki is a ceremonial banner surmounted by a sprig of sakaki.
Here is a photo of masakaki from Kyoto Shingu, a Kyoto-based Shintō religious implements manufacturer and retailer.
Here is a pair of masakaki positioned on either side of an altar.
Now if we are talking about a masakaki, then we are talking about a sacred object that is part of a set tableau with a specific ceremonial purpose. It seems also that a single religious tableau can have only two masakaki in it.
Which makes Prime Minister Abe's and House Speaker Kōno Yōhei's sponsorship of masakaki at Yasukuni a little bit more significant than either of them just sending a nice plant to brighten up the place.
Somebody should check.
Later - OK, I have checked. According to reports the PM indeed paid for a masakaki - which the following Hokkaido Shimbun editorial (Japanese only) helpfully identifies as "a holy offering called a 'masakaki' that was presented as an oblation to the shrine".
Goodbye houseplant. Hello "separation of church and state" dispute.