Context : Polar ring galaxies ( PRGs ) are composed of two kinematically distinct and nearly orthogonal components , a host galaxy ( HG ) and a polar ring/disk ( PR ) .
The HG usually contains an older stellar population than the PR .
The suggested formation channel of PRGs is still poorly constrained .
Suggested options are merger , gas accretion , tidal interaction , or a combination of both .

Aims : To constrain the formation scenario of PRGs , we study the compact stellar systems ( CSSs ) in two PRGs at different evolutionary stages : NGC 4650A with well-defined PR , and NGC 3808 B , which is in the process of PR formation .

Methods : We use archival HST/WFPC2 imaging in the F 450 W,F 555 W , or F 606 W and F 814 W filters .
Extensive completeness tests , PSF-fitting techniques , and color selection criteria are used to select cluster candidates .
Photometric analysis of the CSSs was performed to determine their ages and masses using stellar population models at a fixed metallicity .

Results : Both PRGs contain young CSSs ( < 1 Gyr ) with masses of up to 5 \times 10 ^ { 6 } M _ { \odot } , mostly located in the PR and along the tidal debris .
The most massive CSSs may be progenitors of metal-rich globular clusters or ultra compact dwarf ( UCD ) galaxies .
We identify one such young UCD candidate , NGC 3808 B-8 , and measure its size of r _ { eff } = 25.23 ^ { +1.43 } _ { -2.01 } pc .
We reconstruct the star formation history of the two PRGs and find strong peaks in the star formation rate ( SFR , \simeq 200M _ { \odot } /yr ) in NGC 3808 B , while NGC 4650 A shows milder ( declining ) star formation ( SFR < 10 M _ { \odot } /yr ) .
This difference may support different evolutionary paths between these PRGs .

Conclusions : The spatial distribution , masses , and peak star formation epoch of the clusters in NGC 3808 suggest for a tidally triggered star formation .
Incompleteness at old ages prevents us from probing the SFR at earlier epochs of NGC 4650 A , where we observe the fading tail of CSS formation .
This also impedes us from testing the formation scenarios of this PRG .